PHP allows interaction with a large number of relational database management systems, such as MySQL, Oracle, IBM DB2, Microsoft SQL Server, PostgreSQL and SQLite. PHP runs on most major operating systems, including UNIX, Linux, Windows, and Mac OS X, and can interact with many major web servers. The official PHP website contains very extensive documentation.

There is a command line interface, as well as GUI libraries such as the Gimp Tool Kit (GTK+) and text mode libraries like Ncurses and Newt.

PHP is the result of the efforts of many contributors. It is licensed under the PHP License, a BSD-style license. Since version 4, it has been powered by the Zend engine.

PHP was originally designed as a small set of Perl scripts, followed by a rewritten set of CGI binaries written in C by the Danish-Canadian programmer Rasmus Lerdorf in 1994 to display his résumé and to collect certain data, such as how much traffic his page was receiving. "Personal Home Page Tools" was publicly released on 8 June 1995 after Lerdorf combined it with his own Form Interpreter to create PHP/FI.

Zeev Suraski and Andi Gutmans, two Israeli developers of the Technion - Israel Institute of Technology, rewrote the parser in 1997 and formed the base of PHP 3, changing the language's name to the recursive acronym "PHP: Hypertext Preprocessor". The development team officially released PHP/FI 2 in November 1997 after months of beta testing. Public testing of PHP 3 began immediately and the official launch came in June 1998. Suraski and Gutmans then started a new rewrite of PHP's core, producing the Zend engine in 1999 (a page at www.zend.com states that PHP 3 was powered by Zend Engine 0.5). They also founded Zend Technologies in Ramat Gan, Israel which has since overseen the PHP advances.

In May 2000, PHP 4, powered by the Zend Engine 1.0, was released.

On July 13, 2004, PHP 5 was released, powered by Zend Engine II. PHP 5 includes new features such as PHP Data Objects (PDO) and more performance enhancements taking advantage of the new engine.

Support for objects

Up until version 3, PHP had no object-oriented features. In version 3 basic object functionality was added. The same semantics were implemented in PHP 4 as well as pass-by-reference and return-by-reference for objects but the implementation still lacked the powerful and useful features of other object-oriented languages like C++ and Java.

In version 5, which was released in July 2004, PHP's object-oriented functionality has been very much enhanced and is more robust and complete.

The LAMP architecture (short for Linux, Apache, MySQL, PHP) has become popular in the Web industry as a way of deploying inexpensive, reliable, scalable, secure web applications (the 'P' in LAMP can also stand for Perl or Python).

Examples of PHP applications include phpBB and MediaWiki.

The PHP model can be seen as an alternative to Microsoft's ASP.NET/C#/VB.NET system, Macromedia's ColdFusion system, Sun Microsystems' JSP/Java system, the Zope/Python system, the Mod perl/Perl system, and more recently the Ruby on Rails framework.