A critical review of studies assessing the marginal adaptation of direct placement, plastic restorations is presented. The effects upon adaptation of cavity design and location of cavity margins are examined, together with the effects of differing placement and finishing techniques. Both the choice of restorative material and the use of liners/bases are shown to influence the quality of restoration margins. Techniques used in both in vivo and in vitro assessment are reviewed, however it appears that a wide variety of methodologies exist and the establishment of standard, published criteria for the qualitative assessment of marginal adaptation is recommended.