This paper describes a new generation of actuators for robotic applications, and more generally for machines that are designed to interact with humans. Such actuators, called Variable Impedance Actuators, are designed to achieve fast motion control while guaranteeing safety of human operators in worst-case impact situation. The fundamental innovation is to implement safety by purely mechanical, passive means, to guarantee intrinsic safety, while active control is used to recover performance. The design concept, which is the subject of a patent application, has led to the experimental implementation of a Variable Stiffness Actuator. The effectiveness of the VSA has been recently validated theoretically and experimentally by authors.