Micro electromechanical systems (MEMS) are emerging technology that enables smart and autonomous applications. Capacitive MEMS devices can be utilized to harvest the ambient kinetic (vibration) energy and convert it into electrical energy. Such devices are commonly known as MEMS energy harvesters, which are used to power on mobile electronic systems. The efficiency response of MEMS energy harvesters depends on the careful modelling and designing of the device. In this book, the modelling and designing considerations of high efficient capacitive MEMS harvester are presented.