Publisher Summary This chapter discusses recent progress in the most frequently used magnetic-field microsensors and microelectromechanical systems (MEMS), which are perfectly compatible with microelectronic technologies. It analyzes results and presents information about physical mechanisms of the origin of magnetosensitivity, device designs, sensor characteristics and the methods for their determination, biasing and interface circuits, the means for performance improvement and overcoming the basic transducer limitations, the most current and prospective applications, and development trends. There are very few cases in which magnetic sensor microsystems function in conditions where the gradient of the measured magnetic field is effective over distances comparable to or smaller than the transducer region. The chapter mentions that enhancement of the effective magnetic field in the active zone of a magnetosensor's can be attained with a magnetic flux concentrator. If plastic-encapsulated packages are not used, the inevitable instability in the characteristics of all microsensors can be strongly reduced and the well-known piezoresistance effect and packaging stress can be eliminated.