Aphids are major crop pests and show a high level of phenotypic plasticity. They display a seasonal, photoperiodically-controlled polyphenism during their life cycle. In spring and summer, they reproduce efficiently by parthenogenesis. At the end of summer, parthenogenetic individuals detect the transition from short nights to long nights, which initiates the production of males and oviparous females within their offspring. These are the morphs associated with the autumn season. Deciphering the physiological and molecular events associated with this switch in reproductive mode in response to photoperiodic conditions is thus of key interest for understanding and explaining the remarkable capacity of aphids to adapt to fluctuations in their environment. The present review aims to compile earlier physiological studies, focussing on the neuroendocrine control of seasonal photoperiodism, as well as a series of large-scale transcriptomic approaches made possible by the recent development of genomic resources for the model aphid species: the pea aphid Acyrthosiphon pisum. These analyses identify genetic programmes putatively involved in the control of the initial steps of detection and transduction of the photoperiodic signal, as well as in the regulation of the switch between asexual and sexual oogenesis within embryonic ovaries. The contribution of small RNAs pathways (and especially microRNAs) in the post-transcriptional control of gene expression, as well as the role of epigenetic mechanisms in the regulation of genome expression associated with the photoperiodic response, is also summarized.