Vipera berus, the common European adder, is a snake found in Europe and northern Asia.
Adder may also refer to:
- AA-12 Adder, a Russian air-to-air missile
- Adder (electronics), an electronic circuit designed to do addition
- Adder Technology, a manufacturing company
- Armstrong Siddeley Adder, a late 1940s British turbojet engine
- Blackadder, a series of BBC sitcoms
- Golden Axe: The Revenge of Death Adder, a video game
- HMS Adder, any of seven ships of the Royal Navy
- Any of several groups of venomous snakes
- USS Adder, a US submarine