Nowadays, parthenogenesis has attracted wide attention due to the potential of deriving pluripotent lines. Embryonic stem cells (ESCs), typically derived from the inner cell mass of the mammalian blastocyst, are in fact of fundamental value for developmental research and in both cell and tissue replacement therapy. In this context, a better understanding of the molecular events occurring during the various developmental stages is essential. This book address the in vitro developmental competence of preimplantation ovine embryos produced by in vitro fertilization (IVF) and Parthenogenetic activation (PA) and the expression pattern of panel of genes related to antioxidant protection (Peroxiredoxins- PRDX 1-6), pluripotency (OCT 4 and NANOG) and stress response (HSP 90beta) in both immature and mature oocytes and at various stages of preimplantation ovine embryos produced by in vitro fertilization and Parthenogenetic activation.