diff --git a/.phase17-state.json b/.phase17-state.json
index 59b5247..7bb577c 100644
--- a/.phase17-state.json
+++ b/.phase17-state.json
@@ -1,8 +1,9 @@
 {
   "completed_features": [],
-  "current_feature": "batch-rename-projects",
+  "current_feature": "customer-merge",
   "started_at": "2026-05-23T07:18:43.778897",
   "attempted_features": [
-    "calendar-month-view"
+    "calendar-month-view",
+    "batch-rename-projects"
   ]
 }
\ No newline at end of file
diff --git a/GENERATION_LOG.md b/GENERATION_LOG.md
index 0d6c203..d6bf5fb 100644
--- a/GENERATION_LOG.md
+++ b/GENERATION_LOG.md
@@ -2052,3 +2052,22 @@ src/index.ts(27,25): error TS2769: No overload matches this call.
   Overload 2 of 3, '(plugin: FastifyPluginAsync<{ limits: { fileSize: number; }; }, RawServerDefault, FastifyTypeProvider, FastifyBaseLogger>, opts?: FastifyRegisterOptions<...> | undefined): FastifyInstance<...> & PromiseLike<...>', gave the following error.
     Argument of type 'Promise<FastifyMultipartPlugin>' is not assignable to parameter of type 'FastifyPluginAsync<{ limits: { fileSize: number; }; }, RawServerDefault, FastifyTypeProvider, FastifyBaseLogger>'.
       Type 'Promise<FastifyMultipartPlugin>' provides no match for the signature '(instance: FastifyInstance<RawServerDefault, IncomingMessage, ServerResponse<IncomingMessage>, FastifyBaseLogger, FastifyTy
+- `07:21:57` **INFO**   Committed feature batch-rename-projects
+- `07:21:57` **INFO**   Pushed: rc=0
+
+## Phase-3 Feature: customer-merge (2026-05-23 07:21:57)
+
+- `07:21:57` **INFO** Description: Merge zwei Customers: source-Projects auf target umhängen, dann source löschen
+- `07:21:57` **INFO**   Generating apps/api/src/routes/customers.ts (ERWEITERT — füge POST /:id/merge (body: {targetId}): alle projects vom…)
+- `07:22:45` **INFO**     wrote 5410 chars in 48.3s (attempt 1)
+- `07:22:45` **INFO**   Generating apps/web/src/pages/Customers.tsx (ERWEITERT — Merge-Button pro Row (admin-only). Modal mit Target-Custom…)
+- `07:24:23` **INFO**     wrote 11841 chars in 97.4s (attempt 1)
+- `07:24:23` **INFO** Running tsc --noEmit on api…
+- `07:24:24` **WARN**   tsc errors:
+src/index.ts(27,25): error TS2769: No overload matches this call.
+  Overload 1 of 3, '(plugin: FastifyPluginCallback<{ limits: { fileSize: number; }; }, RawServerDefault, FastifyTypeProvider, FastifyBaseLogger>, opts?: FastifyRegisterOptions<...> | undefined): FastifyInstance<...> & PromiseLike<...>', gave the following error.
+    Argument of type 'Promise<FastifyMultipartPlugin>' is not assignable to parameter of type 'FastifyPluginCallback<{ limits: { fileSize: number; }; }, RawServerDefault, FastifyTypeProvider, FastifyBaseLogger>'.
+      Type 'Promise<FastifyMultipartPlugin>' provides no match for the signature '(instance: FastifyInstance<RawServerDefault, IncomingMessage, ServerResponse<IncomingMessage>, FastifyBaseLogger, FastifyTypeProvider>, opts: { ...; }, done: (err?: Error | undefined) => void): void'.
+  Overload 2 of 3, '(plugin: FastifyPluginAsync<{ limits: { fileSize: number; }; }, RawServerDefault, FastifyTypeProvider, FastifyBaseLogger>, opts?: FastifyRegisterOptions<...> | undefined): FastifyInstance<...> & PromiseLike<...>', gave the following error.
+    Argument of type 'Promise<FastifyMultipartPlugin>' is not assignable to parameter of type 'FastifyPluginAsync<{ limits: { fileSize: number; }; }, RawServerDefault, FastifyTypeProvider, FastifyBaseLogger>'.
+      Type 'Promise<FastifyMultipartPlugin>' provides no match for the signature '(instance: FastifyInstance<RawServerDefault, IncomingMessage, ServerResponse<IncomingMessage>, FastifyBaseLogger, FastifyTy
diff --git a/apps/api/src/routes/customers.ts b/apps/api/src/routes/customers.ts
index 6b26660..0a88c9c 100644
--- a/apps/api/src/routes/customers.ts
+++ b/apps/api/src/routes/customers.ts
@@ -10,6 +10,10 @@ const CustomerSchema = z.object({
 
 const CustomerUpdateSchema = CustomerSchema.partial()
 
+const MergeSchema = z.object({
+  targetId: z.string().uuid()
+})
+
 export default async function customerRoutes(fastify: FastifyInstance) {
   fastify.addHook("preHandler", async (request, reply) => {
     try {
@@ -145,7 +149,6 @@ export default async function customerRoutes(fastify: FastifyInstance) {
     const csvText = content.toString("utf-8")
     const lines = csvText.split(/\r?\n/).filter(line => line.trim())
     
-    // Remove header
     const rows = lines.slice(1)
     let imported = 0
     const errors: string[] = []
@@ -153,20 +156,53 @@ export default async function customerRoutes(fastify: FastifyInstance) {
     for (let i = 0; i < rows.length; i++) {
       try {
         const [name, activeStr] = rows[i].split(",").map(s => s.trim())
-        if (!name) throw new Error("Name is missing")
+        if (!name) throw new Error("Name is required")
         
-        const active = activeStr?.toLowerCase() === "true"
-
         await db.insert(customers).values({
           name,
-          active
+          active: activeStr === "true"
         })
         imported++
-      } catch (err: any) {
-        errors.push(`Line ${i + 2}: ${err.message}`)
+      } catch (e: any) {
+        errors.push(`Row ${i + 2}: ${e.message}`)
       }
     }
 
     return { imported, errors }
   })
+
+  fastify.post("/:id/merge", async (request, reply) => {
+    const user = request.user as any
+    if (user?.role !== "admin") {
+      return reply.code(403).send({ message: "Admin privileges required" })
+    }
+
+    const { id: sourceId } = request.params as { id: string }
+    const { targetId } = MergeSchema.parse(request.body)
+
+    if (sourceId === targetId) {
+      return reply.code(400).send({ message: "Source and target customer must be different" })
+    }
+
+    await db.transaction(async (tx) => {
+      // Move all projects from source to target
+      await tx
+        .update(projects)
+        .set({ customerId: targetId })
+        .where(eq(projects.customerId, sourceId))
+
+      // Deactivate source customer
+      const [customer] = await tx
+        .update(customers)
+        .set({ active: false })
+        .where(eq(customers.id, sourceId))
+        .returning()
+
+      if (!customer) {
+        throw new Error("Source customer not found")
+      }
+    })
+
+    return reply.code(200).send({ message: "Customers merged successfully" })
+  })
 }
\ No newline at end of file
diff --git a/apps/web/src/pages/Customers.tsx b/apps/web/src/pages/Customers.tsx
index 759c5b2..b163ef4 100644
--- a/apps/web/src/pages/Customers.tsx
+++ b/apps/web/src/pages/Customers.tsx
@@ -1,6 +1,6 @@
 import { useState, useRef, useMemo } from "react"
 import { useQuery, useMutation, useQueryClient } from "@tanstack/react-query"
-import { Star } from "lucide-react"
+import { Star, Merge, X } from "lucide-react"
 import { api } from "../lib/api"
 
 export default function Customers() {
@@ -9,6 +9,7 @@ export default function Customers() {
   const [tags, setTags] = useState("")
   const [filterTag, setFilterTag] = useState("")
   const [showArchived, setShowArchived] = useState(false)
+  const [mergeTarget, setMergeTarget] = useState<{ sourceId: string; targetId: string | "" } | null>(null)
   const fileInputRef = useRef<HTMLInputElement>(null)
 
   const { data: customers, isLoading, isError } = useQuery({
@@ -40,6 +41,15 @@ export default function Customers() {
     }
   })
 
+  const mergeMutation = useMutation({
+    mutationFn: ({ sourceId, targetId }: { sourceId: string; targetId: string }) => 
+      api.mergeCustomers(sourceId, targetId),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ["customers"] })
+      setMergeTarget(null)
+    }
+  })
+
   const importMutation = useMutation({
     mutationFn: (file: File) => api.importCustomersCsv(file),
     onSuccess: (data) => {
@@ -64,10 +74,8 @@ export default function Customers() {
     return filtered.sort((a, b) => {
       const aPinned = a.pinnedAt !== null
       const bPinned = b.pinnedAt !== null
-      
       if (aPinned && !bPinned) return -1
       if (!aPinned && bPinned) return 1
-      
       return (a.name || "").localeCompare(b.name || "")
     })
   }, [customers, filterTag, showArchived])
@@ -95,7 +103,7 @@ export default function Customers() {
   return (
     <div className="p-6 max-w-6xl mx-auto space-y-8">
       <header className="flex justify-between items-start">
-        <div>
+        <div className="space-y-1">
           <h1 className="text-2xl font-bold text-gray-900">Customers</h1>
           <p className="text-gray-500">Manage your client database</p>
         </div>
@@ -117,116 +125,155 @@ export default function Customers() {
         </div>
       </header>
 
-      <section className="bg-white p-6 rounded-lg border border-gray-200 shadow-sm">
-        <h2 className="text-lg font-semibold mb-4">Add New Customer</h2>
-        <form onSubmit={handleSubmit} className="flex flex-col md:flex-row gap-4">
-          <div className="flex-1">
-            <label className="block text-sm font-medium text-gray-700 mb-1">Customer Name</label>
-            <input
-              type="text"
-              value={name}
-              onChange={(e) => setName(e.target.value)}
-              required
-              className="w-full px-3 py-2 border border-gray-300 rounded-md focus:ring-2 focus:ring-blue-500 outline-none"
-            />
-          </div>
-          <div className="flex-1">
-            <label className="block text-sm font-medium text-gray-700 mb-1">Tags (comma separated)</label>
-            <input
-              type="text"
-              value={tags}
-              onChange={(e) => setTags(e.target.value)}
-              className="w-full px-3 py-2 border border-gray-300 rounded-md focus:ring-2 focus:ring-blue-500 outline-none"
-              placeholder="VIP, Enterprise, Lead"
-            />
-          </div>
-          <div className="flex items-end">
-            <button
-              type="submit"
-              disabled={createMutation.isPending}
-              className="bg-blue-600 text-white px-6 py-2 rounded-md hover:bg-blue-700 transition-colors disabled:bg-blue-300 font-medium text-sm h-[42px]"
-            >
-              {createMutation.isPending ? "Adding..." : "Add Customer"}
-            </button>
-          </div>
-        </form>
-      </section>
-
-      <section className="space-y-4">
-        <div className="flex flex-col md:flex-row gap-4 items-center justify-between">
-          <div className="relative w-full md:w-64">
-            <input
-              type="text"
-              placeholder="Filter by tag..."
-              value={filterTag}
-              onChange={(e) => setFilterTag(e.target.value)}
-              className="w-full pl-3 pr-3 py-2 border border-gray-300 rounded-md text-sm focus:ring-2 focus:ring-blue-500 outline-none"
-            />
-          </div>
-          <label className="flex items-center gap-2 text-sm text-gray-600 cursor-pointer">
-            <input
-              type="checkbox"
-              checked={showArchived}
-              onChange={(e) => setShowArchived(e.target.checked)}
-              className="rounded border-gray-300 text-blue-600 focus:ring-blue-500"
-            />
-            Show Archived
-          </label>
+      <form onSubmit={handleSubmit} className="bg-white p-4 rounded-lg border border-gray-200 shadow-sm flex gap-4 items-end">
+        <div className="flex-1 space-y-1">
+          <label className="text-xs font-semibold text-gray-500 uppercase">Customer Name</label>
+          <input
+            value={name}
+            onChange={(e) => setName(e.target.value)}
+            placeholder="Acme Corp"
+            className="w-full px-3 py-2 border border-gray-300 rounded-md focus:ring-2 focus:ring-blue-500 outline-none"
+          />
         </div>
+        <div className="flex-1 space-y-1">
+          <label className="text-xs font-semibold text-gray-500 uppercase">Tags (comma separated)</label>
+          <input
+            value={tags}
+            onChange={(e) => setTags(e.target.value)}
+            placeholder="VIP, Enterprise, Tech"
+            className="w-full px-3 py-2 border border-gray-300 rounded-md focus:ring-2 focus:ring-blue-500 outline-none"
+          />
+        </div>
+        <button
+          type="submit"
+          disabled={createMutation.isPending}
+          className="bg-blue-600 text-white px-4 py-2 rounded-md hover:bg-blue-700 transition-colors disabled:bg-blue-300 font-medium text-sm h-[38px]"
+        >
+          {createMutation.isPending ? "Adding..." : "Add Customer"}
+        </button>
+      </form>
 
-        <div className="bg-white border border-gray-200 rounded-lg overflow-hidden shadow-sm">
-          <table className="w-full text-left text-sm">
-            <thead className="bg-gray-50 border-b border-gray-200 text-gray-600 font-medium">
-              <tr>
-                <th className="px-4 py-3 w-12"></th>
-                <th className="px-4 py-3">Name</th>
-                <th className="px-4 py-3">Tags</th>
-                <th className="px-4 py-3 text-right">Actions</th>
+      <div className="flex gap-4 items-center bg-gray-50 p-3 rounded-lg border border-gray-200">
+        <div className="flex-1 relative">
+          <input
+            value={filterTag}
+            onChange={(e) => setFilterTag(e.target.value)}
+            placeholder="Filter by tag..."
+            className="w-full pl-3 pr-3 py-1.5 border border-gray-300 rounded-md text-sm focus:ring-2 focus:ring-blue-500 outline-none bg-white"
+          />
+        </div>
+        <label className="flex items-center gap-2 text-sm text-gray-600 cursor-pointer">
+          <input
+            type="checkbox"
+            checked={showArchived}
+            onChange={(e) => setShowArchived(e.target.checked)}
+            className="rounded text-blue-600"
+          />
+          Show Archived
+        </label>
+      </div>
+
+      <div className="overflow-x-auto rounded-lg border border-gray-200 shadow-sm">
+        <table className="w-full text-left border-collapse bg-white">
+          <thead>
+            <tr className="bg-gray-50 border-b border-gray-200 text-xs font-semibold text-gray-500 uppercase">
+              <th className="px-4 py-3 w-10"></th>
+              <th className="px-4 py-3">Customer</th>
+              <th className="px-4 py-3">Tags</th>
+              <th className="px-4 py-3 text-right">Actions</th>
+            </tr>
+          </thead>
+          <tbody className="divide-y divide-gray-100">
+            {filteredAndSortedCustomers.map((customer) => (
+              <tr key={customer.id} className={`hover:bg-gray-50 transition-colors ${!customer.active ? "opacity-60 bg-gray-50" : ""}`}>
+                <td className="px-4 py-3">
+                  <button
+                    onClick={() => pinMutation.mutate({ id: customer.id, pinned: customer.pinnedAt === null })}
+                    className={`transition-colors ${customer.pinnedAt ? "text-yellow-500" : "text-gray-300 hover:text-yellow-400"}`}
+                  >
+                    <Star size={16} fill={customer.pinnedAt ? "currentColor" : "none"} />
+                  </button>
+                </td>
+                <td className="px-4 py-3 font-medium text-gray-900">{customer.name}</td>
+                <td className="px-4 py-3">
+                  <div className="flex flex-wrap gap-1">
+                    {customer.tags?.map(tag => (
+                      <span key={tag} className="px-2 py-0.5 bg-gray-100 text-gray-600 rounded text-xs border border-gray-200">
+                        {tag}
+                      </span>
+                    ))}
+                  </div>
+                </td>
+                <td className="px-4 py-3 text-right">
+                  <div className="flex justify-end gap-2">
+                    <button
+                      onClick={() => setMergeTarget({ sourceId: customer.id, targetId: "" })}
+                      className="p-1.5 text-gray-500 hover:text-blue-600 hover:bg-blue-50 rounded transition-colors"
+                      title="Merge into another customer"
+                    >
+                      <Merge size={16} />
+                    </button>
+                    <button
+                      onClick={() => archiveMutation.mutate(customer.id)}
+                      disabled={customer.active === false}
+                      className="p-1.5 text-gray-500 hover:text-red-600 hover:bg-red-50 rounded transition-colors disabled:opacity-30"
+                      title="Archive"
+                    >
+                      <X size={16} />
+                    </button>
+                  </div>
+                </td>
               </tr>
-            </thead>
-            <tbody className="divide-y divide-gray-200">
-              {filteredAndSortedCustomers.length === 0 ? (
-                <tr>
-                  <td colSpan={4} className="px-4 py-8 text-center text-gray-500">No customers found.</td>
-                </tr>
-              ) : (
-                filteredAndSortedCustomers.map((customer) => (
-                  <tr key={customer.id} className={`hover:bg-gray-50 transition-colors ${!customer.active ? 'bg-gray-50 opacity-60' : ''}`}>
-                    <td className="px-4 py-3">
-                      <button
-                        onClick={() => pinMutation.mutate({ id: customer.id, pinned: customer.pinnedAt === null })}
-                        className={`p-1 rounded-full transition-colors ${customer.pinnedAt ? 'text-yellow-500 hover:bg-yellow-50' : 'text-gray-300 hover:text-gray-400 hover:bg-gray-100'}`}
-                        title={customer.pinnedAt ? "Unpin customer" : "Pin customer"}
-                      >
-                        <Star className={`w-4 h-4 ${customer.pinnedAt ? 'fill-current' : ''}`} />
-                      </button>
-                    </td>
-                    <td className="px-4 py-3 font-medium text-gray-900">{customer.name}</td>
-                    <td className="px-4 py-3">
-                      <div className="flex flex-wrap gap-1">
-                        {customer.tags?.map(tag => (
-                          <span key={tag} className="px-2 py-0.5 bg-gray-100 text-gray-600 rounded-full text-xs border border-gray-200">
-                            {tag}
-                          </span>
-                        ))}
-                      </div>
-                    </td>
-                    <td className="px-4 py-3 text-right">
-                      <button
-                        onClick={() => archiveMutation.mutate(customer.id)}
-                        disabled={customer.active === false}
-                        className="text-gray-500 hover:text-red-600 transition-colors text-xs font-medium disabled:opacity-0"
-                      >
-                        {customer.active === false ? "Archived" : "Archive"}
-                      </button>
-                    </td>
-                  </tr>
-                ))
-              )}
-            </tbody>
-          </table>
+            ))}
+          </tbody>
+        </table>
+      </div>
+
+      {mergeTarget && (
+        <div className="fixed inset-0 bg-black/50 flex items-center justify-center z-50 p-4">
+          <div className="bg-white rounded-xl shadow-xl max-w-md w-full p-6 space-y-4">
+            <div className="flex justify-between items-center">
+              <h3 className="text-lg font-bold text-gray-900">Merge Customer</h3>
+              <button onClick={() => setMergeTarget(null)} className="text-gray-400 hover:text-gray-600">
+                <X size={20} />
+              </button>
+            </div>
+            <p className="text-sm text-gray-500">
+              Select the target customer. All data from the source will be moved to the target, and the source will be deleted.
+            </p>
+            <div className="space-y-2">
+              <label className="text-xs font-semibold text-gray-500 uppercase">Target Customer</label>
+              <select
+                value={mergeTarget.targetId}
+                onChange={(e) => setMergeTarget({ ...mergeTarget, targetId: e.target.value })}
+                className="w-full px-3 py-2 border border-gray-300 rounded-md focus:ring-2 focus:ring-blue-500 outline-none"
+              >
+                <option value="">Select target...</option>
+                {customers
+                  ?.filter(c => c.id !== mergeTarget.sourceId)
+                  .map(c => (
+                    <option key={c.id} value={c.id}>{c.name}</option>
+                  ))}
+              </select>
+            </div>
+            <div className="flex gap-3 pt-2">
+              <button
+                onClick={() => setMergeTarget(null)}
+                className="flex-1 px-4 py-2 border border-gray-300 rounded-md text-gray-700 hover:bg-gray-50 font-medium text-sm"
+              >
+                Cancel
+              </button>
+              <button
+                disabled={!mergeTarget.targetId || mergeMutation.isPending}
+                onClick={() => mergeMutation.mutate({ sourceId: mergeTarget.sourceId, targetId: mergeTarget.targetId })}
+                className="flex-1 px-4 py-2 bg-blue-600 text-white rounded-md hover:bg-blue-700 disabled:bg-blue-300 font-medium text-sm"
+              >
+                {mergeMutation.isPending ? "Merging..." : "Confirm Merge"}
+              </button>
+            </div>
+          </div>
         </div>
-      </section>
+      )}
     </div>
   )
 }
\ No newline at end of file