diff --git a/src/lib/analytics/gtag.ts b/src/lib/analytics/gtag.ts
new file mode 100644
index 00000000..564d06ef
--- /dev/null
+++ b/src/lib/analytics/gtag.ts
@@ -0,0 +1,64 @@
+// Google Analytics 4 (gtag.js) plumbing.
+//
+// SvelteKit is a single-page app after hydration, so GA's automatic page_view
+// only fires for the very first server response. We disable that automatic hit
+// (`send_page_view: false`) and emit a page_view ourselves on every client-side
+// navigation. See Analytics.svelte for the lifecycle wiring.
+
+type GtagArgs = unknown[];
+
+declare global {
+	interface Window {
+		dataLayer?: GtagArgs[];
+		gtag?: (...args: GtagArgs) => void;
+	}
+}
+
+// The id we have already injected, so initAnalytics is idempotent and
+// setAnalyticsUser knows which config to address.
+let activeId: string | null = null;
+
+/**
+ * Inject gtag.js for `measurementId` and prime the data layer. Browser-only and
+ * idempotent — safe to call from afterNavigate on every navigation. The initial
+ * automatic page_view is disabled; callers emit page_view via trackPageView.
+ */
+export function initAnalytics(measurementId: string, options: { userId?: string | null } = {}): void {
+	if (typeof window === 'undefined' || !measurementId || activeId === measurementId) {
+		return;
+	}
+	activeId = measurementId;
+
+	const script = document.createElement('script');
+	script.async = true;
+	script.src = `https://www.googletagmanager.com/gtag/js?id=${measurementId}`;
+	document.head.appendChild(script);
+
+	window.dataLayer = window.dataLayer ?? [];
+	// gtag forwards its raw argument list onto the data layer; gtag.js reads each
+	// entry by index/length, so pushing the rest array behaves like `arguments`.
+	window.gtag = function gtag(...args: GtagArgs) {
+		window.dataLayer!.push(args);
+	};
+	window.gtag('js', new Date());
+	window.gtag('config', measurementId, {
+		send_page_view: false,
+		...(options.userId ? { user_id: options.userId } : {})
+	});
+}
+
+/** Emit a page_view for the current document/location. No-op until initAnalytics has run. */
+export function trackPageView(path: string): void {
+	if (typeof window === 'undefined' || !window.gtag) return;
+	window.gtag('event', 'page_view', {
+		page_path: path,
+		page_location: window.location.href,
+		page_title: document.title
+	});
+}
+
+/** Align GA's user_id with the logged-in user (pass null on logout). No-op until initAnalytics has run. */
+export function setAnalyticsUser(userId: string | null): void {
+	if (typeof window === 'undefined' || !window.gtag || !activeId) return;
+	window.gtag('config', activeId, { user_id: userId });
+}
diff --git a/src/lib/components/Analytics.svelte b/src/lib/components/Analytics.svelte
new file mode 100644
index 00000000..ea40a9b1
--- /dev/null
+++ b/src/lib/components/Analytics.svelte
@@ -0,0 +1,39 @@
+<script lang="ts">
+	// Google Analytics 4 for app.cropwatch.io.
+	//
+	// Mounted once in the root layout so it covers every route (including /auth).
+	// page_view is emitted on each client-side navigation, and GA's user_id is
+	// kept in sync with the logged-in Supabase user so per-user journeys are
+	// visible across pages and devices. Set PUBLIC_GA_MEASUREMENT_ID to enable;
+	// disabled automatically in dev so local traffic never reaches the property.
+	import { afterNavigate } from '$app/navigation';
+	import { dev } from '$app/environment';
+	import { tick } from 'svelte';
+	import { page } from '$app/state';
+	import { env } from '$env/dynamic/public';
+	import { getAppContext } from '$lib/appContext.svelte';
+	import { initAnalytics, trackPageView, setAnalyticsUser } from '$lib/analytics/gtag';
+
+	const app = getAppContext();
+
+	// env is read inside browser-only callbacks (never at module top level) so it
+	// is never touched during SSR/prerender, which $env/dynamic/public forbids.
+	const measurementId = () => (dev ? '' : (env.PUBLIC_GA_MEASUREMENT_ID ?? ''));
+
+	// Keep GA's user_id aligned with the session `sub` claim. Re-runs on
+	// login / logout / token refresh; no-ops until initAnalytics has run.
+	$effect(() => {
+		const sub = app.session?.sub ?? null;
+		if (measurementId()) setAnalyticsUser(sub);
+	});
+
+	// afterNavigate fires on first mount AND every client-side navigation, so one
+	// handler covers the initial page view and all subsequent ones.
+	afterNavigate(async () => {
+		const id = measurementId();
+		if (!id) return;
+		initAnalytics(id, { userId: app.session?.sub ?? null });
+		await tick(); // let <svelte:head><title> update before reading document.title
+		trackPageView(page.url.pathname + page.url.search);
+	});
+</script>
diff --git a/src/routes/+layout.svelte b/src/routes/+layout.svelte
index 23af5280..54a24cee 100644
--- a/src/routes/+layout.svelte
+++ b/src/routes/+layout.svelte
@@ -16,6 +16,7 @@
 	import { page } from '$app/state';
 	import OverviewDrawer from './OverviewDrawer.svelte';
 	import Sidebar from './Sidebar.svelte';
+	import Analytics from '$lib/components/Analytics.svelte';
 	import { createAppContext, setAppContext } from '$lib/appContext.svelte';
 	import type { DeviceStatusSummary, RuleTemplateDto } from '$lib/api/api.dtos';
 	import type { IJWT } from '$lib/interfaces/jwt.interface';
@@ -114,6 +115,8 @@
 	<meta name="theme-color" content="#1f283b" media="(prefers-color-scheme: dark)" />
 </svelte:head>
 
+<Analytics />
+
 <CwOfflineOverlay labels={cwOfflineOverlayLabels()} />
 <CwToastContainer />