'''Adder''' may refer to:

* [[Adder (snake)]], a family of snakes.
** [[European adder]], a species of adder.
* [[Adder (Farthing Wood)]], a character from ''The Animals of Farthing Wood''.
* [[Adder (electronics)]], a digital circuit designed to do addition.
* [[AA-12 Adder]], a Russian air-to-air missile.
* [[List of Advance Wars COs#Adder|Adder]], a Commanding Officer in the ''Nintendo Wars'' series.
* [[USS Adder (SS-3)]], an early US submarine.

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