Much has been assumed, yet little empirically understood, about men’s sexual desire. The objectives of the current study were to: a) explore, and expand on, the phenomenon of men’s sexual desire, b) gain insight into men’s experiences of sexual desire within, and outside of, their long-term relationships, and c) determine the degree to which men’s experiences of sexual desire correspond to, or deviate from, traditional theories of men’s sexual desire (i.e., Evolutionary Theory, Sexual Script Theory, and Masculinity Theory). Thirty semi-structured interviews with men between the ages of 30 and 65, in long-term heterosexual relationships were included. Analysis was conducted using Grounded Theory Methodology from the constructionist perspective. It was determined that men’s sexual desire was largely relational in nature. Factors determined to elicit sexual desire were: a) Feeling Desired, b) Feeling Sexy, Attractive and Desirable, c) Cognitions and Moods, d) Visual Sexual Cues, e) Exciting and Unexpected Sexual Encounters, f) Context of the Sexual Encounter, and g) Intimate Communication. Factors determined to inhibit sexual desire were: a) Physical Ailments and Negative Health Characteristics, b) Life Pressures and Stresses, c) Sexual Abuse, d) Less Emphasis on and Effort Invested in Sexual Encounters, e) Rejection, f) Partner not Equally Engaged in Sexual Activity, and g) Lack of Emotional Connection with Partner. Sexual desire was also described as occurring extra-relationally, albeit in different ways (i.e., more fleeting, less emotional). Men described their desire for other women as natural and biological, but also indicated that acting on these feelings could, or should, be controlled. Some participants described having high and constant levels of sexual desire. However, most men indicated that their sexual desire was sometimes feigned in order to appear more masculine or reduce the chance of upsetting their female partner. This was due to a felt social pressure to demonstrate certain actions and behaviours that were consistent with traditional sexual scripts and norms. The findings from this study suggest that men’s sexual desire is more complex and relational than previous theoretical models and past research suggest. Implications for researchers and therapists are discussed.