The Northrop Grumman RQ-4 Global Hawk is a high-altitude, remotely-piloted surveillance aircraft introduced in 2001. It was initially designed by Ryan Aeronautical, and known as Tier II+ during development. The RQ-4 provides a broad overview and systematic surveillance using high-resolution synthetic aperture radar (SAR) and electro-optical/infrared (EO/IR) sensors with long loiter times over target areas.

Surveillance aircraft are aircraft used for surveillance. They are primarily operated by military forces and government agencies in roles including intelligence gathering, maritime patrol, battlefield and airspace surveillance, observation, and law enforcement.