Conventional digital halftoning approaches function by modulating either the dot size [amplitude modulation (AM)] or the dot density [frequency modulation (FM)]. Generally, AM halftoning methods have the advantage of low computation and good print stability, while FM halftoning methods typically have higher spatial resolution and resistance to moiré artifacts. In this paper, we present a new class of AM/FM halftoning algorithms that simultaneously modulate the dot size and density. The major advantages of AM/FM halftoning are better stability than FM methods through the formation of larger dot clusters; better moiré resistance than AM methods through irregular dot placement; and improved quality through systematic optimization of the dot size and dot density at each gray level. We present a general method for optimizing the AM/FM method for specific printers, and we apply this method to an electrophotographic printer using pulse width modulation technology.