Agda is a dependently typed functional programming language originally developed by Ulf Norell at Chalmers University of Technology with implementation described in his PhD thesis. The current version of Agda was originally known as Agda 2. The original Agda system was developed at Chalmers by Catarina Coquand in 1999. The current version is a full rewrite, which should be considered a new language that shares a name and tradition. Agda is based on Zhaohui Luo's Unified Theory of Dependent Types (UTT) a type theory similar to Martin-Löf type theory.