The cytoskeletal protein vinculin contributes to the mechanical link of the contractile actomyosin cytoskeleton to the extracellular matrix (ECM) through integrin receptors. In addition, vinculin modulates the dynamics of cell adhesions and is associated with decreased cell motility on two-dimensional ECM substrates. The effect of vinculin on cell invasion through dense three-dimensional ECM gels is unknown. Here, we report how vinculin expression affects cell invasion into three-dimensional collagen matrices. Cell motility was investigated in vinculin knockout and vinculin expressing wild-type mouse embryonic fibroblasts. Vinculin knockout cells were 2-fold more motile on two-dimensional collagen-coated substrates compared with wild-type cells, but 3-fold less invasive in 2.4 mg/ml three-dimensional collagen matrices. Vinculin knockout cells were softer and remodeled their cytoskeleton more dynamically, which is consistent with their enhanced two-dimensional motility but does not explain their reduced three-dimensional invasiveness. Importantly, vinculin-expressing cells adhered more strongly to collagen and generated 3-fold higher traction forces compared with vinculin knockout cells. Moreover, vinculin-expressing cells were able to migrate into dense (5.8 mg/ml) threedimensional collagen matrices that were impenetrable for vinculin knockout cells. These findings suggest that vinculin facilitates three-dimensional matrix invasion through up-regulation or enhanced transmission of traction forces that are needed to overcome the steric hindrance of ECMs.Cell migration is an important and fundamental biomechanical process that plays an essential role in inflammatory diseases, embryonic development, wound healing, and metastasis formation. Current concepts of cell migration have been established in two-dimensional models, but they can explain only partially the migratory behavior in three dimensions. For instance, the migratory capability of cells on two-dimensional substrates depends mainly on adhesion strength, adhesion dynamics, and the dynamics of cytoskeletal remodeling (1, 2), whereas the migratory capability of cells in three-dimensional connective tissue depends also on the steric hindrance of the matrix, matrix degradation by proteolytic enzyme secretion, and the generation of protrusive or contractile forces (1, 3-5). The balance of all these parameters-adhesion strength, cytoskeletal remodeling, matrix degradation, and the generation and transmission of contractile forces-is important for the migration speed in three-dimensional extracellular matrix (ECM) 2 (6). Depending on this balance, a broad variety of invasion strategies between different cell types and even within the same cell type are possible (7).The connection between the ECM and the actomyosin cytoskeleton through integrin-type cell-matrix adhesion receptors is facilitated by the mechano-coupling protein vinculin (8, 9). The effect of vinculin on the migration of cells has previously been investigated using two-dimensional ECM substrates, whe...