The endometrium is a complex multicellular tissue that undergoes dynamic alterations under the control of ovarian-derived sex steroid hormones. During the proliferative phase of the human menstrual cycle, oestrogen induces proliferation of the endometrial epithelium while during the progesterone-dominated secretory phase, the endometrial stromal compartment differentiates in preparation for pregnancy. This differentiation event is termed decidualisation and it is accompanied by immune cell infiltration, vascular remodelling and secretion of cytokines and growth factors, as well as a newfound capacity of active steroid synthesis in the endometrium. Defective decidualisation has been described in several endometrial-associated disorders such as endometriosis, a pathology of ectopic endometrial tissue in the peritoneal cavity, often associated with infertility. Rodent models have been used for the investigation of endometrial physiology and pathology due to the similarity in uterine tissue architecture, appropriate endometrial responses to steroid hormones and the opportunity to inform cellular mechanisms using genetic manipulation. While the impact of 17β-oestradiol and progesterone on endometrial function have been extensively studied, androgens have only recently emerged as potent potential regulators of the endometrium, however, their impact on cell function has not been fully elucidated. The aims of this study were to: Identify the impact of androgens on endometrial function using a mouse model of steroid depletion (ovariectomy) followed by administration of the potent androgen dihydrotestosterone (DHT). Investigate the capacity of endometrial stromal cells to synthesise androgens during decidualisation using human primary endometrial stromal cells (hESCs) decidualised in vitro. Elucidate the decidualisation response of hESCs from women with endometriosis after modulation of androgen receptor (AR) function during decidualisation. Novel results obtained provided evidence of a role for androgens in inducing a trophic effect in the mouse uterus characterised by: pronounced endometrial epithelial proliferation, altered expression pattern of AR, changes in the expression of genes involved in cell-cycle progression and stromal-epithelial cross-talk. In addition, androgen treatment resulted in a striking and unexpected increase in the number of endometrial glands. Decidualisation of hESCs resulted in time-dependent changes in expression of the androgen synthesising enzymes AKR1C3 and 5α-reductase (accompanied by biosynthesis of both testosterone and DHT in a dynamic time-dependent manner). Notably, blocking of AR action arising from local androgen signalling during decidualisation of hESCs culminates in sub-optimal decidualisation as detected by the expression of the classical decidualisation markers IGFBP1 and PRL. Women with endometriosis are reported to exhibit defective decidualisation, which may be accompanied with infertility. Treatment of hESCs from women with endometriosis with an AR agonist (DHT) or antagonist (flutamide) during decidualisation resulted in striking differences in decidualisation response as demonstrated in a case-study approach. Taken together, these findings highlight novel roles of androgens in regulating endometrial function by impacting on cell proliferation, gland formation and decidualisation. These striking new findings have implications for endometrial disorders such as endometriosis. Future studies will focus on the use of selective androgen receptor modulators, a novel class of compounds, with tissue-selective actions and without the undesired side-effects of potent androgens. The use of AR modulators would benefit from a personalised medicine approach, instructed by patient profiling to direct therapeutic targeting of endometrial disorders.