Abstract: The initial-value formulation of General Relativity constitutes an important method for constructing and studying solutions of the theory. The initial-data needed for Cauchy evolutions cannot be freely specified in their entirety. Rather they are subject to certain constraint equations which must be satisfied. I discuss how to construct initial-data, which can be used to describe black holes. Then I use such initial-data to calculate several physical properties. In particular, I sketch how to compute the interaction energy for two well seperated spinless black holes.