301 redirect
A 301 redirect is a server instruction that permanently sends one URL to another, so anyone (or any search engine) arriving at the old address lands on the new one. It's the mechanism that carries a page's accumulated ranking value across a URL change.
In practice
The number is an HTTP status code, and the distinction that matters is permanent versus temporary. A 301 says "this moved for good, update your records." A 302 says "this is a temporary detour, keep the old address." Search engines treat them differently, and using a 302 for a permanent move is one of the quieter ways a site loses ground after a rebuild.
Rankings belong to URLs, not to companies. That single fact is why redirects matter more than almost anything else in a website migration. If /services/precision-machining/ has spent six years earning its position and the new site puts that content at /capabilities/machining/, the old URL has to point at the new one. Without that, the new page starts from zero and the old one starts returning a 404.
The failure mode is rarely a missing redirect map. It's a partial one. Teams map the top twenty pages, launch, and discover months later that a few hundred deeper URLs were dropped, each of which was quietly bringing in a handful of visits. Those pages tend to be the specific, long-tail ones a technical buyer actually searched for.
Two habits keep redirects healthy. Redirect to the closest equivalent page, not to the homepage: a buyer who wanted a specific capability and lands on your homepage has to start their search again, and search engines increasingly treat a mass redirect to the homepage as a soft 404. And avoid chains, where A points to B which points to C. Each hop costs a little speed and a little link equity, and long chains sometimes stop being followed at all.
A test you can run before any launch: export every URL from your current site, put it in a spreadsheet next to its destination on the new one, and sort by the ones you left blank. If that blank column has entries you can't account for, the redirect map isn't finished, and a redesign is the most common way a site loses its rankings.
Common questions
What is the difference between a 301 and a 302 redirect?
A 301 is permanent and tells search engines to transfer the old URL's ranking value to the new one. A 302 is temporary and tells them to keep indexing the original. Use a 301 for anything that has genuinely moved for good.
Do 301 redirects pass SEO value?
Yes. A 301 passes the large majority of the original URL's ranking signals to the destination. That transfer is the entire reason redirects are non-negotiable during a redesign or platform move.
Can I just redirect all my old pages to the homepage?
You can, and it's a common shortcut, but it costs you. Search engines often treat a bulk redirect to the homepage as a soft 404 and pass little value, and a visitor who wanted one specific page has to start over. Map each URL to its closest equivalent.
How long should redirects stay in place?
Indefinitely, in practice. Old links on other people's websites, in PDFs, and in email signatures keep sending traffic for years. Removing a redirect breaks every one of those.