One of the most important features of portable electronic devices has become their power consumption, which directly affect their working time. One of the ways to accurately monitor and control power dissipation is to measure current going from the battery into separate power converters and further to different peripherals. The accurate sensing of each current portion gives better information of which device consumes more power and gives more opportunities for both internal and external control to limit the loss. The aim of this work is to analyze the main power sources and their current measurement techniques in portable electronic devices and propose a realization of highly accurate and flexible current measurement solution integrated on the same chip with the power device and which would be able to accurately monitor all ingoing current from the main supply and outgoing current into peripherals. This book can be of help to both design and system engineers targeting high performance, low power portable applications for different markets ranging from low cost consumer electronics to highly dependable and robust systems.