In the last few years, the adoption and worldwide proliferation of clinical procedures for medically assisted conception have been associated with the examination and analysis of spermatozoa, oocytes and early embryos under a variety of in vivo and in vitro conditions. These analyses have enabled correlations to be made between the behavior of gametes, the pattern of early embryonic development and the initiation of a normal pregnancy. Collectively, the findings have not only enormously increased our understanding of the process of early human development, but also have provided new insights into the origin and causes of reproductive failure in man. The research presented in this volume describes recent results derived from the study of normal and abnormal patterns of human spermatogenesis, oogenesis and early embryogenesis. The chapters discuss aberrations in morphodynamic and morphophysiological processes that have clinical relevance in human infertility and conception. Two of the chapters describe, respectively, the basic research that allows the cryopreservation of human oocytes and embryos, and the development of in vitro systems that permit the study of cell differentiation and interaction during the peri-implantation period. When relevant, each chapter extrapolates findings from in vitro experimentation to the comparable situation that is observed in vivo.