Large individual differences in cooperative contributions are common within animal societies such as cooperative breeders, where helpers care for offspring which are not their own. Understanding this variation has been a major focus in behavioural ecology and while evidence has shown that individuals are capable to adaptively adjust their cooperative behaviours, the physiological mechanisms underlying such adjustments remain poorly understood. Steroid hormones are prominent candidates to regulate cooperative behaviours due to their ability to integrate internal physiological state and environmental stimuli to produce an adaptive behavioural response. In this thesis, I investigate the effects of two steroid hormones, Cortisol (CORT) and Testosterone (T), in the regulation of cooperative behaviours in the Damaraland mole-rat (Fukomys damarensis). Because these hormones are susceptible to both modulate and be modulated by cooperative contributions, I experimentally tested both sides of this relationship. I show that, despite the absence of correlation between CORT and T and cooperative contributions, experimental increases of cooperative contributions elevate CORT levels, but not T (Chapter 3). Additionally, experimental increases of CORT levels in female helpers raised their cooperative contributions by more than one half demonstrating the regulatory effect of CORT on cooperative behaviours (Chapter 4). As breeding opportunities are likely to affect cooperative contributions and because T is a likely candidate to mediate a trade-off between future reproduction and current cooperation, I tested the effects of experimental increases of T levels in female helpers. I show that such elevations have no measurable effect of aggression, dispersal tendencies (both important to attain a breeding position) or cooperative contributions (Chapter 5). Taken together, the results of this thesis demonstrate that CORT can both respond to and regulate cooperative behaviours and suggest that this hormone may play a major role in the adaptive regulation of cooperative behaviour.