A generalization of assignment games, called partitioning games, is introduced. Given a finite set N of players, there is an a priori given subset pi of coalitions of N and only coalitions in pi play an essential role. Necessary and sufficient conditions for the non-emptiness of the cores of all games with essential coalitions pi are developed. These conditions appear extremely restrictive. However, when N is “large,” there are relatively few “types” of players, and members of pi are “small” and defined in terms of numbers of players of each type contained in subsets, then approximate cores are non-empty.