摘要： Male infertily is a contributing factor in up to 50% of all infertility cases, a solo cause in about 30% of them. Therefore, new and improved diagnostic methods that reduce operator variability regarding sperm defects that are not accesible by the conventional microscope scoring should be evaluated. Assisted reproductive technology (ART) has been involved in the description of alternative pathways in basic cellular functions. it is important to know that it is also related to the peri-implantatory processes that involve the sperm-oocyte interaction, cellular changes observed during fertilization, and the early and late embryo development. Several pathways have been involved at the early stages of human gametogenesis. The spermatozoon has demonstrated an intricate correlation during the fertilization process, as a transfected vector on genetic material, and as interacting with other inner components (RNAm, mitochondrial organelles, etc.). Spermatogenesis is affected by programmed death cell pathways from its packaging process through the elongated cytoplasmic structures during spermiogenesis. Flow cytometry (FC) has been an outstanding tool with the capability to select human gametes to achieve a better reproductive condition. It has been applied as a diagnostic and therapeutic tool allowing a measurable and objective selection and discrimination of spermatozoa from subfertile subjects. Using FC, we are able to know that early distribution of organelles such as mitochondria has an impact in embryo quality before genetic activation on the eight-cell stages occurs. This chapter will let the readers know the current knowledge on sperm fertilization and the relation between the embryo development and the offspring and all the tools now available for an early diagnosis and to identify therapeutic options with FC.