  The first step in the building of a spacetime solution of Einstein's
gravitational field equations via the initial value formulation is finding a
solution of the Einstein constraint equations. We recall the conformal method
for constructing solutions of the constraints and we recall what it tells us
about the parameterization of the space of such solutions. One would like to
know how to construct solutions which model particular physical phenomena. One
useful step towards this goal is learning how to glue together known solutions
of the constraint equations. We discuss recent results concerning such gluing.
