Density has been historically vital to the idea of the city, and has emerged as a central concern in relation to urban social justice and the climate emergency. Indeed, it has become near-impossible to think the politics of the urban present – and future – without it. How, then, should we understand the nature, potential and limits of density in the city today? In this presentation, I argue that three inter-related concerns matter here. First, urban density needs to be understood in the context of a relational geography of transformation, sociospatial inequality, and ecological crisis. Second, density matters not only as an abstraction and measurement, but in its relation to citylife itself, ie, to being, experiencing, and perceiving forms of living that are urban, including the potential for more progressive and inclusive citylife. Third, density opens up a particular entry point to the urban political, especially in relation to the idea of the (offline and online) ‘crowd’, which is becoming increasingly important to the expression of urban social and ecological change.