The orbital environment has so deteriorated to such a serious extent that space activities must comply with the world debris mitigation guidelines, the UN Debris Mitigation Guidelines, for example. However, the recent intentional destruction of spacecraft, the accidental break-up of spent rocket bodies, and orbital collisions among satellites are accelerating the deterioration. Now, world experts are seeking active debris removal that will be essential in the near future to ensure the sustainability of space activities. This article describes the recent debris environment, the risk of debris impact, and the necessity of debris removal.