Multiple-input-multiple-output (MIMO) technology is a key feature and the most promising technology to truly reach the promised transfer data rates of 5G communications. Compared with previous generations, a large number of antenna elements, operating concurrently, is expected to be applied for 5G mobile handsets. The book "MIMO Antenna Systems for 5G Mobile Handsets" outlines the design, simulation, fabrication, and measurements of several diversity MIMO antenna arrays with multiple elements and improved characteristics for 5G mobile handset applications. Various designs of single-band, multi-band, and broad-band MIMO antennas with dual-polarization and reduced mutual coupling function have been designed and their properties are investigated. In addition, the impacts of user-hand/user-head and SAR levels are studied.