PDA stands for Personal Digital Assistant, a handheld device (small and light enough to be operated while it is held in the hands) that is typically used as a personal organizer. It has evolved into a more complicated computer-like gadget capable of performing a multiplicity of functions, such as serving as wireless communicators for sending and receiving data, faxes, and electronic-mail messages. The PDA concept was first introduced by Apple's MessagePad in 1993, and was later revolutionized by the PalmPilot in 1996, created by Palm, Inc. The overall market for PDAs has now grown by 20.7% in the third quarter of 2005, compared to the third quarter of 2004.

A basic PDA features a date book, address book, task list, memo pad, clock, and calculator software. Today, PDAs are widely used as notepads, word processors, spreadsheets, and appointment schedulers and to synchronize data with a PC or home computer. They may also be integrated with cell phones to provide mobile communication and be used for accessing the Internet through technologies such as Wi-Fi, Wide-Area Networks (WANs), and Bluetooth.

Most PDA devices are not equipped with a keyboard like palmtop computers. Instead, they are pen based and rely on special hardware that recognizes handwritten inputs to tap selections on menus and enter printed characters. Some devices may also include an on-screen keyboard for better accessibility.

PDAs now depend largely on a number of Operating Systems to function. Some of the most widely used PDA Operating Systems include Palm OS (Palm, Inc); Windows Mobile (Microsoft); Blackberry (Research in Motion); Symbian OS; and those based on the Linux kernel available for free such as GPE, and OPIE/Qtopia.