Implantation failure and inadequate placental development are important contributors to infertility, recurrent miscarriage, and other pregnancy-related problems in women. Better understanding of these processes is hampered by the difficulty in obtaining human tissue from which primary cells can be prepared and by the very limited access worldwide to human blastocysts for experimentation. Therefore, the use of appropriate cell lines, particularly for functional studies of implantation and placentation, is imperative. While a number of cell lines for both endometrium and trophoblast have been developed and are widely used, it is difficult for researchers to decide which of these are most appropriate for studies of particular functions. This brief review summarizes the known phenotypes of the most widely used cell lines and indicates which might be the most appropriate for individual studies.