A mobile device (or handheld computer) is a computer, small enough to hold and operate in the hand. Mobile devices typically have a flat LCD or OLED screen, a touchscreen interface, and digital or physical buttons. They may also have a physical keyboard. Many such devices can connect to the Internet and connect with other devices such as car entertainment systems or headsets via Wi-Fi, Bluetooth, cellular networks or near field communication. Integrated cameras, the ability to place and receive voice and video telephone calls, video games, and Global Positioning System (GPS) capabilities are common. Power is typically provided by a lithium-ion battery. Mobile devices may run mobile operating systems that allow third-party applications to be installed and run.

Early smartphones were joined in the late 2000s by larger tablets. Input and output are usually via a touch-screen interface. Phones/tablets and personal digital assistants may provide much of the functionality of a laptop/desktop computer in addition to exclusive features. Enterprise digital assistants can provide additional business functionality such as integrated data capture via barcode, RFID and smart card readers.

By 2010, mobile devices often contained sensors such as accelerometers, magnetometers and gyroscopes, allowing the detection of orientation and motion. Mobile devices may provide biometric user authentication, such as face recognition or fingerprint recognition.

Major global manufacturers of mobile devices are Samsung, Huawei, Meizu, Zte, Xiaomi, Sony, Google, HTC, LG, TCL, Motorola Mobility, Nokia, Realme and Micromax Informatics.