People who have depression whilst they are adolescents are more likely to have depression, and other health problems, in later life. They are also more likely to face social and economic challenges. When measuring depression, it is usual to gauge the average levels of depressive symptoms, such as negative emotions, someone has: for example, are they high, or rising quite steeply? In addition, though, evidence suggests that how variable one’s mood is may also be important in predicting later health and other outcomes: for example, does someone’s mood fluctuate a lot, around these average levels? However, whilst a lot of research has been focused on trying to better understand average levels of mood, there have been far fewer studies exploring such variability in mood. This project aims to help address this, by focusing on variability in depressive symptoms from childhood through to early adulthood, with the aim of forming a fuller understanding of the development of depression, beyond average levels of symptoms.