A 301 redirect is an HTTP status code indicating that a resource has been permanently moved to a new URL. When a server responds with a 301 status, it includes a Location header specifying the new URL. Browsers automatically follow the redirect, and search engines transfer the original URL's ranking signals to the new destination.
The 301 redirect is the most important redirect type for SEO. When a page moves permanently, a 301 redirect ensures that the link equity accumulated by the old URL is passed to the new one. Google has confirmed that 301 redirects pass full PageRank to the destination, making them the recommended choice for permanent URL changes such as site migrations, domain changes, and URL structure updates. SEO migration books on Amazon cover these strategies.
In URL shortening, 301 redirects are used when the short URL is intended to be a permanent alias for the destination. Since browsers cache 301 redirects, subsequent visits to the same short URL may bypass the shortening service entirely, which improves speed but reduces the accuracy of click tracking.
The trade-off between 301 and 302 redirects is a key design decision for URL shortening services. A 301 is better for SEO but harder to track, while a 302 preserves tracking accuracy but does not pass link equity. Many services default to 301 for branded links and 302 for campaign links. Web server administration books on Amazon discuss configuration details.