The cerebellum is one of the first brain structures to begin to differentia
te, yet it is one of the last to achieve maturity - the cellular organizati
on of the cerebellum continues to change for many months after birth. This
protracted developmental process creates a special susceptibility to disrup
tions during embryogenesis and makes the cerebellum highly amenable to stud
y. Over the past few years, genetic research has provided a great deal of i
nformation about the molecular events directing the formation of the cerebe
llum. Knowledge of these mechanisms should enable us to address the nature
of human diseases that have their root in developmental processes.