This paper introduces the first monolithic integration of a 3-axis accelerometer, a 2-axis magnetometer and a fullcustom front-end electronics. This complete Inertial Measurement Unit (IMU) has been designed on a single die of 7.5mm² in a 0.35μm CMOS technology. The five electromechanical sensors are batch-manufactured using a single-step wet etching of the CMOS die. Compared to existing Inertial Measurement Units, assembly costs and common issues associated with sensor misalignments are suppressed. Sensors make use of resistive transduction, either mechanically or thermally induced. The on-chip electronic has been designed to cancel parasitic effects such as offset and to optimize the signal to-noise ratio on each measurement axis. The achieved performance (8-bits on Earth magnetic field measurement, 8- bits and 6-bits on x/y and z gravity acceleration respectively) makes the device suitable for numerous applications in consumer electronics.