This paper outlines the rationale of the Fundamentals Underlying Number (F. U. N.) program, and describes Unit I, which is primarily intended for nursery and kindergarten children. This unit develops concepts for sets, numbers, and relations. Each major concept is broken into finely sequenced levels, and at each level instruction is through two basic games: "Find It" (the child identifies an example of the concept) and "Make It" (the child constructs an example of the concept). Procedures for playing these games, the special materials used, the concepts covered, and the spiraling of the sequence are all illustrated in this paper. (MM)