More than 100 years ago, histologists had already detected “fibers” within cells including the mitotic spindle and generally recognised the existence of a “cytomatrix”, although there was much controversy about whether or not the fibers observed were created by chemical fixation. As a result of the application of electron microscopy in the 1960s and especially fluorescence microscopy in the 1970s, it became clear that vertebrate cells generally contain a structural framework composed of three types of protein polymers: actin filaments, microtubules and intermediate filaments. Together this network has been termed the “cytoskeleton”. Unlike the bones of the skeleton that support our body, the polymers of the cytoskeleton are continuously assembled and disassembled to modulate the form and interactions of cells, according to their specific functions. We will be concerned here with the role of the cytoskeleton in cell movement and related motile processes.