Adipose tissue is complex and heterogeneous; in the normal lean state, white fat is composed of roughly 50% adipocytes and 50% other cell types, such as endothelial cells, pre-adipocytes, fibroblasts, and immune cells. In obesity, the ratio of non-adipocytes: adipocytes can rise to as high as 10:1! Understanding adipose tissue biology thus requires a detailed accounting of the constituent cell types and how they change according to factors like depot type, sex, age, nutritional status, or ambient temperature. We are building a large single cell atlas of mouse and human adipose tissue across a range of depots and conditions, using techniques like Drop-seq, DroNc-seq, and 10X. We have already identified several new cell types and are investigating novel functions for many established cell types. In addition, we are piloting projects in spatial transcriptomics, to identify how these different cell types associate with one another in three-dimensional space. We collaborate on this project with Linus Tsai (BIDMC), Aviv Regev (Broad), Diane Mathis (HMS), and others.