Small Unmanned Aerial Vehicles (UAVs) are an emerging class of targets in our skies due to their proliferation in recent years, both supporting new capabilities and economic activities (inspections, professional filming, monitoring, delivery, search and rescue) and potentially enabling accidental or deliberate misuses (privacy violation, collision hazard, hostile reconnaissance, smuggling, weaponised UAVs). There is no book yet on radar technologies being developed to counter them.