About 460 OB associations were selected by a comparison of theUBV plates. TheUBV photographic photometry of 1944 blue stars in the associations was made. The new associations appear like cores within Humphreys and Sandage's associations. Their star content, size distribution, and mean size ≈80 pc confirm their identity with the OB associations in the Galaxy and in the Magellanic clouds. The boundaries of the associations are delineated mainly by the density of the resolved stars on theU plates. It is impossible to divide them into smaller areas. The genuine OB associations form groups of two or more members with a length scale of 250 pc. Their boundaries were delineated independently, but they coincide with the OB associations of Humphreys and Sandage (1980). These groups represent real concentration of blue massive stars with a large age dispersion. The star complexes unify a group of associations,Hii regions, andHi peak distribution. Their mean size is 570 pc. The extensiveHi clouds with a mean size of 1.2 kpc contain two or more star complexes. The questions related to star formation are briefly discussed.