Controlling the force exchanged between a robot manipulator and the environment during the physical interaction is crucial for the successful execution of a number of practical tasks both in industrial and service robotics. The chapter focuses on basic control problems related to interaction control of robot manipulators with static/dynamic environments or with humans. It starts from the analysis of impedance control, conceived to keep the contact forces limited by ensuring a suitable compliant behavior to the robot without requiring an accurate model of the environment. The coupled stability and performance of the interacting systems is analyzed by using the concept of passivity, starting from simple linear examples. Then, the problem of interaction tasks modeling is considered, in the case of rigid environments of known geometry imposing constraints to the robot motion, as well as in the case of compliant environments of elastic type. This formulation leads to the synthesis of hybrid force/motion control schemes.