.co is the Internet country code top-level domain (ccTLD) assigned to Colombia.

It is administered by .CO Internet S.A.S., a strategic venture formed between Arcelandia S.A. (which has interests in a variety of Internet-related businesses) and Neustar, Inc (a provider of global registry and managed DNS services for top-level domains). As of July 10, 2010, there are no registration restrictions on second-level .co domains; any individual or entity in the world can register a .co domain. Some examples of .co use include Twitter (t.co), AngelList (Angel.co), ENTER (Enter.co), 500 Startups (500.co), Aspen Group (Aspen.co), and Google Inc. (g.co). Some companies such as American Express (amex.co) and Starbucks (sbux.co) are using .co for URL shortening in social media.