Cyber-physical systems are under constant and increasing attacks as components of the critical infrastructure. Additive manufacturing systems are a new class of cyber-physical systems that produce threedimensional objects layer by layer. Agencies and companies such as NASA, the European Space Agency, General Electric and SpaceX have explored a broad range of application areas for additive manufacturing, including creating functional parts of safety-critical systems such as jet engines. The range of application areas and dependence on computerization makes additive manufacturing an attractive target for attackers.This chapter focuses on attacks that seek to change the physical properties of additive-manufactured components. Such attacks can weaken, damage or destroy manufactured components and, in scenarios where weak or damaged components are used in safety-critical systems, potentially endanger human lives. Attacks intended to damage additive manufacturing equipment and additive manufacturing environments are also discussed.