Sensors and devices, based on micromachining technology, known as micro-electro-mechanicalsystems or MEMS, have been received increasing attention so far in recent years. Micromachined inertial sensors, consisting of accelerometers and gyroscopes, are one of the most important types of silicon-based sensor. MEMS capacitive accelerometers have been extensively used in automobiles, inertial navigation systems, earth quake detection and many other bio-medical applications. This book deals with the design of a monolithic 3DOF MEMS capacitive accelerometer using both analytical and numerical techniques. Monolithic accelerometer is a single structure having three individual single axis Accelerometers on a single substrate and utilizes a surface micromachining technology using standard PolyMUMPs process. The designed accelerometer is 3mm×3.1mm in size, has low mechanical noise floor, high sense capacitance and high sensitivity along in-plane (x and y) and out-of-plane (z) axes. Performing a detailed finite element analysis in ANSYS 11.o, physical level simulation has been done to verify the deflection for x, y and z axes with respect to the applied acceleration (g).