Аннотация:The OB association in the Galaxy, the LMC, M31, and M33 are typically 200-300 pc in diameter; they often represent groupings of several components. Star complexes are twice the size of OB associations, on the average; the presence of Cepheids and O stars implies that the members of complexes may have an age dispersion of up to 6 x 10 to the 7th yr. Within complexes and large associations, denser regions approximately 100 pc across with approximately 1 x 10 to the 7th yr age dispersion may occur; their stars presumably originated from a common giant molecular cloud. Some complexes show evidence of a discrete age distribution, perhaps testimony to star formation through Parker instability.