A 404 status code tells the browser that the server successfully received the request but can't locate the resource at that specific URL. Unlike a 500-series server error, the server itself works fine—the problem is the content doesn't exist at that address. Common causes include deleted pages, mistyped URLs, broken internal or external links, moved content without redirects, or outdated bookmarks. When Google crawls a 404, it doesn't immediately harm your rankings, but large numbers of 404s waste crawl budget and create poor user experience. A handful of 404s on old blog posts or discontinued products is normal; hundreds appearing suddenly usually means a migration gone wrong or a broken navigation element. How you handle 404s matters more than their existence. If the content genuinely doesn't exist and has no logical replacement, serving a proper 404 is correct—don't redirect every dead page to your homepage, which dilutes link equity and confuses users. If the page moved, use a 301 redirect to the new location. If it's temporarily gone, use 410 (Gone) to tell search engines it's intentionally removed and won't return. Your 404 page itself should help users navigate back to useful content. Include a search box, links to main categories, and maybe popular pages. We design 404 pages that match site branding and give clear next steps rather than generic "page not found" text. Monitor 404s in Google Search Console under the Coverage report and in server logs. Prioritize fixing 404s that receive external backlinks (you're wasting link equity) or high traffic from internal links (broken navigation). For Ottawa SEO's portfolio sites, we run monthly broken-link audits using Screaming Frog, filtering for pages that return 404 but still get internal links or external referring traffic. Fix those first—redirect to relevant alternatives or restore the content if it had value.