This chapter focuses on segregation phenomena in urban contexts–that is, situations in which different population groups do not enjoy the same access to what a city has to offer. While there are “macroscopically”-enforced types of segregation, such as what existed under the apartheid regime in South Africa, segregation also appears through emergence in the complex system formed by the web of interactions that connects individuals’ decisions on where they choose to live, work and play within the city. Here, we provide a brief introduction to various aspects of segregation: its multiple definitions and dimensions, available data sources (from traditional surveys and censuses to digital human traces), indices and other types of measure, and finally, a selection of approaches to study and analyze segregation.