  Higher Homotopy van Kampen Theorems allow the computation as colimits of
certain homotopical invariants of glued spaces. One corollary is to describe
homotopical excision in critical dimensions in terms of induced modules and
crossed modules over groupoids. This paper shows how fibred and cofibred
categories give an overall context for discussing and computing such
constructions, allowing one result to cover many cases. A useful general result
is that the inclusion of a fibre of a fibred category preserves connected
colimits. The main homotopical application are to pairs of spaces with several
base points, but we also describe briefly the situation for triads.
