Recent studies have elucidated both the mechanism of early formation of div
erse muscle fibre types and the matching of diverse populations of motoneur
ons to their appropriate muscle targets. Highlights include the demonstrati
on that distinct signals are necessary for the formation of several distinc
t myoblast populations in the vertebrate somite, the identification of moto
neuron subtypes, studies of how motoneurons target appropriate muscles, and
rapid progress on the Drosophila neuromuscular system. We propose a model
in which four classes of decision control the patterning of both motoneuron
s and muscles.