Our social identities are at the heart of who we are, affecting our thoughts, emotions, attitudes, and behaviour. However, there are still many unanswered questions about how social identities develop and interact with each other outside laboratory settings. In this talk, I will introduce a novel method that uses natural language data to understand which of two social identities are salient at a particular moment in time. I will then demonstrate how this method can be used to understand how new social identities develop: first, with a study on the development of a parent identity in first-time pregnant women, and second a study of opioid addicts in recovery. Next, I will discuss a set of studies that uses language to examine how effective a switch between two social identities is, and how much control we have over such switches. Finally, I will argue that we can also use natural language to understand what the core values of a social group are, and the extent to which these change over longer periods of time.