diff --git a/client/lib/arm-affiliation-service.ts b/client/lib/arm-affiliation-service.ts
new file mode 100644
index 00000000..c662534a
--- /dev/null
+++ b/client/lib/arm-affiliation-service.ts
@@ -0,0 +1,197 @@
+import { supabase } from "./supabase";
+
+export interface ArmAffiliation {
+  arm: "foundation" | "gameforge" | "labs" | "corp" | "devlink";
+  detected: boolean;
+  reason: string;
+  activityCount: number;
+}
+
+/**
+ * Detects which arms a user is affiliated with based on their activities
+ */
+export const armAffiliationService = {
+  /**
+   * Check if user has enrolled in any Foundation courses
+   */
+  async hasFoundationActivity(userId: string): Promise<{ detected: boolean; count: number }> {
+    try {
+      const { data: enrollments, error } = await supabase
+        .from("course_enrollments")
+        .select("id", { count: "exact" })
+        .eq("user_id", userId)
+        .limit(1);
+
+      if (error) throw error;
+      return { detected: (enrollments?.length ?? 0) > 0, count: enrollments?.length ?? 0 };
+    } catch (error) {
+      console.error("Error checking Foundation activity:", error);
+      return { detected: false, count: 0 };
+    }
+  },
+
+  /**
+   * Check if user has GameForge projects/teams
+   */
+  async hasGameForgeActivity(userId: string): Promise<{ detected: boolean; count: number }> {
+    try {
+      const { data: projects, error: projectError } = await supabase
+        .from("gameforge_projects")
+        .select("id", { count: "exact" })
+        .eq("user_id", userId)
+        .limit(1);
+
+      if (projectError) throw projectError;
+
+      const { data: teams, error: teamError } = await supabase
+        .from("gameforge_team_members")
+        .select("id", { count: "exact" })
+        .eq("user_id", userId)
+        .limit(1);
+
+      if (teamError) throw teamError;
+
+      const totalCount = (projects?.length ?? 0) + (teams?.length ?? 0);
+      return { detected: totalCount > 0, count: totalCount };
+    } catch (error) {
+      console.error("Error checking GameForge activity:", error);
+      return { detected: false, count: 0 };
+    }
+  },
+
+  /**
+   * Check if user has Labs research activities
+   */
+  async hasLabsActivity(userId: string): Promise<{ detected: boolean; count: number }> {
+    try {
+      const { data: research, error } = await supabase
+        .from("labs_research_tracks")
+        .select("id", { count: "exact" })
+        .eq("user_id", userId)
+        .limit(1);
+
+      if (error) throw error;
+      return { detected: (research?.length ?? 0) > 0, count: research?.length ?? 0 };
+    } catch (error) {
+      console.error("Error checking Labs activity:", error);
+      return { detected: false, count: 0 };
+    }
+  },
+
+  /**
+   * Check if user has Corp-related activities
+   */
+  async hasCorpActivity(userId: string): Promise<{ detected: boolean; count: number }> {
+    try {
+      // Corp activities could include partnerships, investments, or business accounts
+      const { data: accounts, error } = await supabase
+        .from("corp_accounts")
+        .select("id", { count: "exact" })
+        .eq("user_id", userId)
+        .limit(1);
+
+      if (error) throw error;
+      return { detected: (accounts?.length ?? 0) > 0, count: accounts?.length ?? 0 };
+    } catch (error) {
+      // Corp table may not exist yet, return false
+      return { detected: false, count: 0 };
+    }
+  },
+
+  /**
+   * Check if user has DevLink/Roblox development activity
+   */
+  async hasDevLinkActivity(userId: string): Promise<{ detected: boolean; count: number }> {
+    try {
+      const { data: devLinkProfiles, error } = await supabase
+        .from("devlink_profiles")
+        .select("id", { count: "exact" })
+        .eq("user_id", userId)
+        .limit(1);
+
+      if (error && error.code !== "42P01") throw error; // Ignore table not found errors
+      return { detected: (devLinkProfiles?.length ?? 0) > 0, count: devLinkProfiles?.length ?? 0 };
+    } catch (error) {
+      // Table may not exist yet
+      return { detected: false, count: 0 };
+    }
+  },
+
+  /**
+   * Detect all arm affiliations for a user
+   */
+  async detectAffiliations(userId: string): Promise<ArmAffiliation[]> {
+    const [foundation, gameforge, labs, corp, devlink] = await Promise.all([
+      this.hasFoundationActivity(userId),
+      this.hasGameForgeActivity(userId),
+      this.hasLabsActivity(userId),
+      this.hasCorpActivity(userId),
+      this.hasDevLinkActivity(userId),
+    ]);
+
+    return [
+      {
+        arm: "foundation",
+        detected: foundation.detected,
+        reason: foundation.detected ? `${foundation.count} course(s) enrolled` : "No courses enrolled",
+        activityCount: foundation.count,
+      },
+      {
+        arm: "gameforge",
+        detected: gameforge.detected,
+        reason: gameforge.detected ? `${gameforge.count} project(s) and team(s)` : "No projects or teams",
+        activityCount: gameforge.count,
+      },
+      {
+        arm: "labs",
+        detected: labs.detected,
+        reason: labs.detected ? `${labs.count} research track(s)` : "No research tracks",
+        activityCount: labs.count,
+      },
+      {
+        arm: "corp",
+        detected: corp.detected,
+        reason: corp.detected ? `${corp.count} corp account(s)` : "No corp accounts",
+        activityCount: corp.count,
+      },
+      {
+        arm: "devlink",
+        detected: devlink.detected,
+        reason: devlink.detected ? "DevLink profile created" : "No DevLink profile",
+        activityCount: devlink.count,
+      },
+    ];
+  },
+
+  /**
+   * Sync detected affiliations to user_arm_affiliations table
+   */
+  async syncDetectedAffiliations(userId: string, token: string): Promise<void> {
+    try {
+      const detectedArms = await this.detectAffiliations(userId);
+
+      for (const affiliation of detectedArms) {
+        if (affiliation.detected) {
+          await fetch(`${import.meta.env.VITE_API_BASE}/api/user/arm-affiliations`, {
+            method: "POST",
+            headers: {
+              Authorization: `Bearer ${token}`,
+              "Content-Type": "application/json",
+            },
+            body: JSON.stringify({
+              arm: affiliation.arm,
+              affiliation_type: "courses", // Generic type for auto-detected
+              affiliation_data: {
+                detected: true,
+                reason: affiliation.reason,
+              },
+              confirmed: false,
+            }),
+          });
+        }
+      }
+    } catch (error) {
+      console.error("Error syncing arm affiliations:", error);
+    }
+  },
+};