Аннотация:Observations of the multi-shell complexes around stellar associations Cyg OB1, Cyg OB3 (Lozinskaya etal., 1998) and its comparison to complexes around Ori OB1/u Ori; Car OB1, Car OB2; and Sco OB1 suggest a new approach to the problem of triggering star formation on the space scale of 100-500 pc. The data indicate that a rich OB association can produce a set of expanding shells: a massive slow-expanding one swept-up by stellar winds of MS stars and several fast inner shells produced by the activity of WR stars and, later, by supernova explosions. We argue that the dynamical structures of this type provide favorable conditions for triggering star formation. Under these conditions, two basic physical mechanisms of star formation - gravitational fragmentation and shock compression - can act together in the most effective combination, enhancing each other.