A mobile browser is a web browser designed for use on a mobile device such as a mobile phone or PDA. Mobile browsers are optimized to display Web content most effectively on small screens on portable devices. Mobile browser software must be small and efficient to accommodate the low memory capacity and low-bandwidth of wireless handheld devices. Traditional smaller feature phones use stripped-down mobile web browsers; however, most current smartphones have full-fledged browsers that can handle the latest web technologies, such as CSS 3, JavaScript, and Ajax.

Websites designed to be usable in mobile browsers may be referred to as wireless portals or collectively as the Mobile Web. Today, over 75% of websites are "mobile friendly", by detecting when a request comes from a mobile device and automatically creating a "mobile" version of the page, designed to fit the device's screen and be usable with a touch interface, for example the Wikipedia website (see illustration).