.com is a generic top-level domain (gTLD) used on the Internet's Domain Name System. It was one of the original top-level domains, established in January 1985, and has grown to be the largest TLD in use. It is currently operated by VeriSign. It is consistently pronounced as a word, dot-com, and has entered the common language this way. This is in keeping with the pattern that has emerged for most gTLDs; they are almost always pronounced as words, with the exceptions of .edu, .int, and sometimes .org. However, most country code top-level domains are spelled out, such as .uk, .ca, or .au, to cite just a few examples.

Although .com domains have always been intended for commercial use, they are currently available for anyone to register. In the 1990s, .com became the most common top-level domain for websites, especially commercial ones, and gave its name to dot-com companies. The introduction of .biz, which is restricted to businesses, has had little impact on the popularity of .com.

There has been a tendency since the mid-1990s for companies to include the "dot-com" as part of their official company names, peaking around 2000 (the time known as the "dot-com boom"). This has reduced in frequency since then, however, due to a backlash against this boom and its subsequent bust. On rare occasions, a company or organization will take on an official name including another domain ending, such as .org (ex: OpenOffice.org), but this is much rarer than the .com usage.

Although companies anywhere in the world can register .com domains, many countries have a second-level domain with a similar purpose under their own ccTLD. Such second-level domains are usually of the form .com.xx or .co.xx, where xx is the ccTLD. Australia (.com.au), the United Kingdom (.co.uk), Mexico (.com.mx), New Zealand (.co.nz), People's Republic of China (.com.cn), Japan (.co.jp), South Korea (.co.kr), and India (.co.in) are all examples.

Often, noncommercial sites such as those of nonprofit organizations, governments, and so on will use .com addresses, which some find to be contrary to the domain's original purpose. A .org, .gov, or other more specific TLD might be more appropriate for such sites.