Cells in our body live in a 3-dimensional and often squishy world. Much of what we know about cell biology is based on studies of cells cultured on petri dishes, or rigid flat sheets of plastic. However, mammalian cells in soft tissues function in 3D microenvironments, which are soft and viscoelastic, and in which cells are surrounded by neighboring cells and an extracellular matrix. Importantly, cells sense and respond to the mechanical properties and dimensionality of the microenvironment, and a 3D microenvironment can be confining, serving as a physical barrier to processes such as cell migration or division that involve shape change or growth. We are interested in elucidating the mechanics of cell-matrix interactions in soft tissues. We seek to understand how the mechanical properties of the extracellular matrix regulate processes such as breast cancer progression, stem cell differentiation, and cell division. Further, we aim to determine the biophysics of cell migration and division in confining 3D microenvironments. Our approach involves the use of engineered biomaterials for 3D cell culture and instrumentation to measure forces at the microscale relevant to cells.