Cells use cytoskeletally-generated force to adhere, migrate and remodel their environment. While cellular forces generated by cells plated on 2D substrates is well-studied, much less is known about the forces generated by cells in 3D matrices, which more closely mimic the in vivo environment. Here, an approach to characterize cellular forces in 3D using confocal reflectance microscopy is presented. Remodeling of collagen fibrils due to the forces exerted by embedded cells was imaged in real-time as cells adhere to and contract the matrix. We implemented this approach in conjunction with 2D Traction Force Microscopy to compare cytoskeletally-mediated forces of cells in 3D collagen matrices to forces exerted by cells on 2D collagen-coated hydrogel substrates. Our results indicate that confocal reflectance microscopy of collagen fibrils can provide semi-quantitative information regarding cellular force in 3D matrices, and that the actin cytoskeleton plays a similar role in regulating cell contractility in both 2D and 3D microenvironments.