The delicate nature of reproduction is evidenced by the fact that the female gamete is notorious for having high rates of chromosomal abnormalities. It is estimated 10-25% of all human conceptions are chromosomally abnormal due to an error in chromosome segregation during meiosis. Furthermore, studies indicate greater than 95% of this human aneuploidy is attributable to defects within the meiotic machinery of the oocyte, rather than that of the sperm. This results in chromosomal non-disjunction leading to embryonic aneuploidy, miscarriage, infertility and congenital defects. Nevertheless, causative factors and intraoocyte biochemical signaling pathways causing these chromosomal perturbations are unknown. Therefore, elucidating regulatory mechanisms involved in oocyte meiosis is imperative to fully understand this complex process and establish potential therapies to circumvent oocyte derived embryonic aneuploidies. This book will review the origin, as well as development and growth of the oocyte. Furthermore, major mechanistic and cellular events occurring during oocyte meiosis critical to ensure proper development and cellular ploidy will be discussed, focusing on the role of reversible phosphorylation in control of these processes.