External mechanical forces and forces generated within the cell influence the cytoskeletal organization and play a critical role in cell migration, division, growth and apoptosis. Thus, it is important to understand how the structural organization of the cytoskeleton affects the mechanical properties of the cell. In eukaryotic cells, the most abundant cytoskeletal protein is actin. Under specific conditions monomeric actin polymerizes to form filaments with an approximate diameter of 7-nm and lengths ranging from hundreds of nanometers to few micrometers. In vivo, the organization of F-actin into higher-order structures is regulated by a wide variety of actin binding proteins (ABPs), which are spatially diverse throughout the cell body. For instance, cross-linking proteins localized in the vicinity of the plasma membrane, like filamin, promote the formation of an isotropic F-actin network, known as the cortex, that provides and maintains the structural integrity of the cell. On the other hand, bundling proteins present in the cytoplasm, including -actinin, form thick F-actin cables that transmit contractile forces along the cell during locomotion and help maintain the cell under a pre-stress state. Our group is developing a multi-scale approach for studying F-actin and ABP interactions ranging from network macromechanics to single molecule biophysics. Report on our actin machinery work.