Moral psychology was shaped around three categories of agents and patients: humans, other animals, and supernatural beings. Rapid progress in Artificial Intelligence has introduced a fourth category for our moral psychology to deal with: intelligent machines. Machines can perform as moral agents, making decisions that affect the outcomes of human patients, or solving moral dilemmas without human supervi- sion. Machines can be as perceived moral patients, whose outcomes can be affected by human decisions, with important consequences for human-machine cooperation. Machines can be moral proxies, that hu- man agents and patients send as their delegates to a moral interaction, or use as a disguise in these interactions. Here we review the exper- imental literature on machines as moral agents, moral patients, and moral proxies, with a focus on recent findings and the open questions that they suggest.