The resistance of certain magnetic multilayers decreases by a factor of two with the application of a magnetic field. The discovery of this so-called giant magnetoresistance effect has led to an explosion in research in magnetic multilayers. In part, this research is motivated by the use of this effect in magnetic field sensors and read heads for magnetic disks. It has lead to the discovery of many other interesting phenomena related to spin transport in these systems. These include magnetic exchange coupling that oscillates in sign as layer thicknesses are varied and the ability to reverse the magnetization of a layer by the spins carried by a current passing through the layer. In this talk, I will describe giant magnetoresistance, oscillatory exchange coupling, and spin transfer torques, review the important experiments, and describe simple models of these phenomena.