This paper presents results on the modeling and control of a long towed cable. The cable is divided into cable elements connected by depth actuators. Each cable element is modeled as a three-dimensional string, where the cable is allowed to possess nonlinear tension. The passivity properties of the cable element are established. Exponetial decay of energy in the coupled transversal motion of the cable element is achieved by boundary control in the presence of vanishing perturbations. When subjected to nonvanishing perturbations, the energy growth in the cable is shown to be upper bounded. A cascaded cable system is then considered, and the passivity properties of the cascaded cable system are established. Using Lyapunov’s direct method, asymptotic decay of energy is achieved in the cascaded system with passive controllers applied at the connection points.