MicroRNAs are the major class of gene regulating molecules playing pivotal roles at post-transcriptional level. Two subsequent studies on miRNA are presented here. The 1st study aims to identify and characterize miRNAs in bovine ovary through cloning, expression analysis and target prediction. The 2nd study aimed to elucidate the difference in expression profile of miRNAs in the placenta at day 50 derived from Somatic cell nuclear transfer, in vitro production and artificial insemination pregnancies by quantifying 377 miRNAs and other systematic procedures. The study reveals a massive deregulation of miRNAs which were poorly reprogrammed and affected as large chromosomal cluster as well as miRNA families in the NT and IVP placenta compared to that of AI. Identified deregulation of miRNAs might associate to the abnormal placentogenesis in NT or IVP pregnancies, which are the results of aberrant genetic and epigenetic modification. Altogether, this Book describes the discovery of miRNAs and their functional networks in the bovine ovary and elucidates the pattern of expression of miRNAs along with their regulatory mechanism in the placenta derived from pregnancies of various origins.