The members of the Src family of nonreceptor tyrosine kinases (SFKs) are implicated in multiple signaling processes that regulate key cellular functions, including proliferation, migration, differentiation, and survival. SFKs are activated by a large number of receptors for growth factors, cytokines, steroid hormones, G protein-coupled receptors, and also by adhesion proteins and other signaling partners. Through their common modular kinase an adapter protein domains, SFKs critically contribute to diversify different signal inputs, weaving a complex and dynamic network of cellular responses. Not surprisingly, SFKs are involved in embryo development and in the maintenance of different adult tissues and organs. Conversely, dysfunction of SFKs is associated with different pathologies, including cancer. Despite the continuous research in the field, several aspects of SFKs regulation and function are still not well defined and new roles for these proteins are steadily reported. The aim of this review is to provide an update on the major regulatory mechanisms of SFKs activity, including the emerging redox-dependent pathway. We have also focused on the functional implications of SFKs in Prolactin signaling and breast cancer development, two increasingly important aspects of SFKs biology. Finally, we briefly revisited the role of SFKs during embryo development and provide insights on the involvement of these proteins in the regulation of embryonic, somatic, and breast cancer stem cells.