Tight coupling between biochemical and mechanical properties of the actin cytoskeleton drives a large range of cellular processes including polarity establishment, morphogenesis, and motility. This is possible because actin filaments are semi-flexible polymers that, in conjunction with the molecular motor myosin, can act as biological active springs or “dashpots” able to exert or resist against force in a cellular environment. To modulate their mechanical properties, actin filaments can organize into a variety of architectures generating a diversity of cellular organizations. I will describe the feedback loop between biochemical and mechanical properties of actin organization at the molecular level in vitro, I will integrate this knowledge into our current understanding of cellular actin organization and its physiological roles.