Background There is an increasing research interest in conceptualizations of mental illness, examined in association with help‐seeking, stigma and treatment preferences. A recent focus on young people's concepts has been identified, with depression being one of the most examined conditions. Methods The purpose of this systematic review is to synthesize evidence on children and adolescents' conceptualizations of depression, adopting the model of illness representations. The review further aims to examine developmental trends, gender differences and the role of experience. A systematic review and narrative meta‐synthesis were conducted, reviewing 36 studies identified through a systematic search of six databases in March 2016. Results Thirty‐six quantitative and qualitative studies were included. Half of the young people are able to recognize depression, and recognition increases when symptoms are more severe (e.g. suicidality). Young people are able to name a variety of causes for depression. Mental health professionals are considered the appropriate source of help by half of the young people, followed by family and peers. However, stigma constitutes a major barrier to help‐seeking. There are developmental trends and gender differences in young people's conceptualization of depression, while experience with depression is associated with a broader conceptualization. Conclusions Young people's concepts of depression resemble aspects of adult conceptualizations, however are sometimes incomplete. Further research on younger children and clinical populations is needed. Research on young people's conceptualizations informs both clinical practice and mental health literacy interventions.