Magnetically controlled swarms of microscopic robots might one day help fight cancer inside the body, new research suggests. Over the past decade, scientists have shown they can manipulate magnetic forces to guide medical devices within the human body, as these fields can apply forces to remotely control objects. For instance, prior work used magnetic fields to maneuver a catheter inside the heart and steer video capsules in the gut. Previous research also used magnetic fields to simultaneously control swarms of tiny magnets. In principle, these objects could work together on large problems such as fighting cancers. However, individually guiding members of a team of microscopic devices so that each moves in its own direction and at its own speed remains a challenge. This is because identical magnetic items under the control of the same magnetic field usually behave identically to each other. Now, scientists have developed a way to magnetically control each member of a swarm of magnetic