  Schwinger's algebra of selective measurements has a natural interpretation in
terms of groupoids. This approach is pushed forward in this paper to show that
the theory of coherent states has a natural setting in the framework of
groupoids. Thus given a quantum mechanical system with associated Hilbert space
determined by a representation of a groupoid, it is shown that any invariant
subset of the group of invertible elements in the groupoid algebra determines a
family of generalized coherent states provided that a completeness condition is
satisfied. The standard coherent states for the harmonic oscillator as well as
generalized coherent states for f-oscillators are exemplified in this picture.
