The Apache HTTP Server, commonly referred to as Apache is web server software notable for playing a key role in the initial growth of the World Wide Web.In 2009 it became the first web server software to surpass the 100 million website milestone.

Apache was the first viable alternative to the Netscape Communications Corporation web server (currently named Oracle iPlanet Web Server), and since has evolved to dominate other web servers in terms of functionality and performance[citation needed]. Typically Apache is run on a Unix-like operating system.

Apache is developed and maintained by an open community of developers under the auspices of the Apache Software Foundation. The application is available for a wide variety of operating systems, including Unix, FreeBSD, Linux, Solaris, Novell NetWare, Mac OS X, Microsoft Windows, OS/2, TPF, and eComStation. Released under the Apache License, Apache is open-source software.

Apache was originally based on NCSA HTTPd code. The NCSA code has since been removed from Apache, due to a rewrite.
Since April 1996 Apache has been the most popular HTTP server software in use. As of March 2012 Apache was estimated to serve 57.46% of all active websites and 65.24% of the top servers across all domains.