Single cells sense their environment with remarkable precision. At the same time, cells have diverse mechanisms for communicating. How are sensing and communication connected? I will describe recent theoretical and experimental results that explore this question, including a detailed study of gradient detection by groups of epithelial cells. I will show how communication allows cells to perform new behaviors that single cells cannot perform alone. Moreover, I will demonstrate that simple physical arguments impose fundamental limits to the precision of sensing, and that these limits are altered by cell-cell communication. This work extends the study of cellular information processing to collective ensembles.