This document provides an overview of mobile operating systems. It discusses what a mobile phone is and how mobile OSs operate devices similarly to desktop OSs. The major mobile OSs covered are Symbian, Android, BlackBerry OS, Windows Mobile, and MeeGo/Tizen. Symbian had the largest market share but has declined, while Android is now the dominant leader followed by iOS. The document outlines the history and key features of these various operating systems.