The literature on urban segregation contains a vast array of measures to assess levels of segregation and track change over time. A smaller body of research has sought to draw attention to the demographic processes by which changes in segregation occur. Process studies decompose changes in segregation by examining the many underlying demographic flows at work. These include external exchanges which add people to or remove them from the population of a city, and internal changes which contribute to the rearrangement of the population within the city. A better appreciation of these processes could play a significant role in understanding why cities are moving along different segregation trajectories in the face of similar external pressures. The chapter provides an overview of the process literature, drawing on a range of studies conducted primarily in the European context. It examines the motivations for this work, sets out the methodologies used to decompose changes at city and neighbourhood levels, and summarises some of the main results obtained. Process studies force us to recognise the inherent dynamism of urban locations, often underestimated in popular and academic thinking about cities. They show how gradual structural changes in segregation can be traced back to these demographic processes, and how these processes are in turn influenced by a wide range of social, historical, political and economic factors operating at many different scales. These insights can aid the development of better theoretical models and more informed urban policy interventions.