The power requirements of automotive alternators are increasing significantly due to the introduction of new vehicle electrical loads. Moreover, the possible transition to a 42 V electrical system is introducing new concerns regarding the load dump overvoltage transient of alternators. This thesis makes several contributions to the power density, efficiency, and transient performance of future alternators. A comparison and design optimization of four alternator types is conducted to identify the least cost alternator that meets the challenging requirements of future automobiles. Alternator designs with conventional diode rectifiers and switched-mode rectifiers are investigated. It is found that optimized Lundell alternators are capable of meeting the demands of future systems, and that wound field synchronous machines may also be competitive. It is also found that incorporation of a simple switched-mode rectifier enables substantial improvements in designs optimized for their use. The behavior of the Lundell alternator under load dump transient conditions is studied. It is found that rotor eddy currents limit the rate at which the machine can be de-excited to terminate the transient overvoltage. Models for the de-excitation process are developed based on experimental measurements, and new field control circuits are proposed that provide fast field de-excitation.