I shall present a program for the classification of simply connected, closed, smooth 7-manifolds and extensive results in this program. The program is an extension of M. Kreck's modified surgery applied at the ``2-type''. In particular, it yields a global context for the numerous classifications of classes of 7-manifolds with H_2(M) = Z due to, for example, Kreck and Stolz, Kruggel, Astey-Mica-Pastor, Milgram and Escher. A sample result is the following: Let G and H be finitely generated abelain groups and let p be an element of H. The number of homeomorphism types of simply connected, closed, smooth 7-manifolds with H_2(M) = G and H^4(M) = H, p_1(M) = p is infinite if and only if the rank of G is greater than 1.