Classical steroid hormones (SHs) - estrogens, androgens, progestins, glucocorticoids and mineralocorticoids - play critical roles in the regulation of reproduction, metabolism and cancer. SHs act via their cognate steroid hormone receptors (SHRs) in multiple target tissues throughout the body, exerting their physiological effects through nuclear receptor (NR)-mediated gene transcription. Since SHRs are the mediators of steroid hormone signalling in cells, regulation of their expression and function is critical for appropriate physiological responses to SHs. Cells regulate SHRs by determining the cellular concentration of SHR proteins in the cell and by tightly regulating their activity through post-translational modifications and interactions with coactivator protein complexes. In this chapter we will examine each of these regulatory mechanisms and assess their functional impact on the activity of SHRs.