In aviation, instrument meteorological conditions (IMC) are weather conditions that require pilots to fly primarily by reference to flight instruments, and therefore under instrument flight rules (IFR), as opposed to flying by outside visual references under visual flight rules (VFR). Typically, this means flying in cloud or poor weather, where little or nothing can be seen or recognised when looking out of the window. Simulated IMC can be achieved for training purposes by wearing view-limiting devices, which restrict outside vision and force the trainee to rely on instrument indications only.

Flight instruments are the instruments in the cockpit of an aircraft that provide the pilot with data about the flight situation of that aircraft, such as altitude, airspeed, vertical speed, heading and much more other crucial information in flight. They improve safety by allowing the pilot to fly the aircraft in level flight, and make turns, without a reference outside the aircraft such as the horizon. Visual flight rules (VFR) require an airspeed indicator, an altimeter, and a compass or other suitable magnetic direction indicator. Instrument flight rules (IFR) additionally require a gyroscopic pitch-bank, direction and rate of turn indicator, plus a slip-skid indicator, adjustable altimeter, and a clock. Flight into instrument meteorological conditions (IMC) require radio navigation instruments for precise takeoffs and landings.