Active debris removal
Missions that capture a dead object already in orbit and bring it down, rather than merely avoiding it.
Avoiding debris manages the symptom; removal is the only approach that reduces the total. The hard part is not the capture but the target: a derelict has no docking fixture, no power, and usually tumbles unpredictably, so a servicing spacecraft must match the motion of an object that was never designed to be caught. Spent upper stages are the priority precisely because they are massive - removing one prevents thousands of potential fragments.
The field is small enough that it maps onto individual companies. Of the 21 companies profiled on this site, only one was founded specifically to do this work, and our reporting follows an Astroscale spacecraft aimed at removing an 11-metre spent upper stage, launching on a vehicle from a different newcomer rather than an established provider.
Collision avoidance, which moves the live satellite and leaves the debris exactly where it was, and end-of-life deorbiting, where a satellite disposes of itself using its own propulsion.