in order to perform their functions, many cells must crawl through a complex environment, including neighboring cells and a confining extracellular matrix. this environment can modify their behavior. i will show that simple physical models can describe a wide variety of these complex cell motions, including collective rotations of confined cells, anomalously large persistence of cells in microchannels, and turning instabilities in crawling cells. these models, which link cell shape, polarity (an internal cell compass), and physical forces, show how different environments (and a few other factors) can lead to distinct types of cell motility.