Human actions are affected by "motor contagions"; implicit effects on an observer's actions caused by viewing other people's actions. Though these contagions are ubiquitous, affecting speech, gestures, everyday movements and sports, the mechanisms underlying them are still not fully understood. In this chapter we will review the known forms of motor contagion and show that they can be characterized into two types. First, action driven contagions, which include most previous contagion reports and which manifest as similarities between specific features (like the kinematics, outcome or goal) of an individual's action, and an action they observe. Second, prediction driven contagions, which we define here and which have only recently begun to be explored, are driven by differences between predictions of how another will act and observations of how they actually do act. These lead to implicit modifications of the motor representations in an individual but may not manifest as similarities between action features. We will explore the conceptual mechanisms that can explain these contagions and propose an extension to the previously suggested Dual Route Model of sensorimotor processing so as to explain the entire contagion spectrum. Finally, in the light of this characterization, we will discuss possible strategies to control, prevent and compensate for motor contagions, and optimize performance by athletes.