The basic physical principles involved in the operation of monolithic magnetic sensors are reviewed and technological aspects outlined. More or less conventional devices based on Hall effect, magnetoresistance or current path deflection are described. It is shown that such sensors with 2, 3, 4 or 5 terminal contacts are achievable with standard silicon integrated circuit process. Several kinds of magnetodiodes (p+nn+,p+n, Schottky, MOS, memory, CMOS) have been fabricated on Si and on SOS films and present attractive properties. Finally, the magneto-transistor family is discussed with emphasis to split-terminals, CMOS, unijunction and fila-mentary devices.