  We define and study fibrations of topological groupoids. We interpret a
groupoid fibration L->H with fibre G as an action of H on G by groupoid
equivalences. Our main result shows that a crossed product for an action of L
is isomorphic to an iterated crossed product first by G and then by H. Here
groupoid action means a Fell bundle over the groupoid, and crossed product
means the section C*-algebra.
