The use of polymeric matrix-based composites has become more widespread in the last twenty years. In particular, reinforced thermoplastic systems are the most rapidly growing class of composites. For this reason, there is an extensive amount of literature available on this subject. This review will focus only on the subjects which directly pertain to and provide insight into the effects of thermal history during lamination and cooling on the final degree of crystallinity, morphology, and mechanical properties of such prepregged or laminated composites. It should be noted that our interest in this review is with composites based on semicrystalline matrices with continuous, unidirectional fiber reinforcements unless otherwise stated. In addition, there is an emphasis on polyether ether ketone (PEEK) carbon fiber composites in this review. This is due to the fact that most of the investigations reported in the literature involved the examination of this particular composite system. While there are some specific features of the behavior of PEEK, it is believed that the general concepts discussed with respect to this matrix resin certainly apply to semicrystalline matrix resins in general.