Fourteen ordinary chondrites have been investigated by the 40Ar/39Ar dating technique. At least nine meterorites show degassing ages less than 600 m.y., which are interpreted as the times of major collisional events among meteorite parent objects, probably in the asteroid belt. These nine meteorites experienced collisional degassing of 89--98% of their radiogenic 40Ar, but in no case was the degassing complete. Therefore individual whole rock K-Ar ages are inaccurate measurements of the times of collisional events. Obvious groupings of degassing ages among chondrites exist. Examples of both H and L chondrites show ages of ~40 and ~300 m.y. Several L chondrites show ages of ~500 m.y. One H chondrite gives an age of ~600 m.y., and an LL chondrite gives an age of ~420 m.y. Other less well defined degassing ages are also suggested by the data, including possible ages of ~2000 m.y. Clearly, several collisional events involving several parent objects were involved. All 14 meteorites had previously been studied for shock and reheating effects and classified from lightly to very heavily shocked and from lightly to very heavily reheated. The lightly shocked and reheated Sutton and Wellington H chondrites have lost no 40Ar and give plateau ages of 4.5--4.6 acons. Several meteorites which are moderately to heavily shocked and reheated give reasonable plateau ages through ~60% of rht 39Ar(K) release and high-age 'tails' up to ~ acons for the remainder of the 39Ar release. An inverse correlation is observed between degree of reheating and fraction of 40Ar retained after the impact event. 40Ar/39Ar release profiles are clearly associated with a high K/Ca phase for the plateau ages and a low K/Ca phase for the incompletely reset ages, the indication being that two different minerals are largely determining the nature of the release profiles. Two meteorites which have been very strongly shocked and reheated, Kimble Co. and Ramsdorf, show 40Ar/39Ar release profiles which have been almost completely reset by collisions. However, the very strongly shocked and reheated Rose City H chondrite, which has been extensively melted, gives a complex 40Ar/39Ar release ranging from 0.4 to 2.5 acons and does not yield a plateau. Shock-induced phase transformations and Ar remobilization may have occurred in Rose City and produced the complex release.