Abaddon is an encryption method in which each plaintext letter is encoded in three of the characters þ, ¥, and µ, respectively. Other characters are also used in variations of this code.

For example, to disguise the type of code, the dot, minus, and space could be used to simulate Morse code.

Due to the three characters used, a maximum of 27 characters can be encoded.

Abaddon is a monoalphabetic monographic substitution.