We survey the happiness and economics field to systematize the explanations of the happiness gender gap, whose puzzling evidence stands out both synchronically and diachronically. Further, this analysis is completed by an interdisciplinary review of competing perspectives, mostly from psychology and medical sciences. Beside disciplinary specificities and differences, results and explanations also reveal some intriguing commonalities. Psychology and medical sciences (also assisted by cutting-edge medical technologies) lead in the static (time-invariant) explanation of happiness and its gender gap, while economic works are better equipped to detect external factors and the role of time-varying objective life conditions. In particular, the happiness and economics field has provided original evidence on the country and time-variant nature of the happiness gender gap. Finally, different disciplines have uncovered the common stylized fact that women are increasingly worse off during their life, through aging, with respect to men: its full explanation still remains at the centre of the research agenda.