A Blue Card 「ブルーカード Burū Kādo」 is an algorithm that is used to evolve Digimon in Digimon Tamers.
The Blue Card was first shown in DT01, in which Matsuda Takato inadvertently used it to convert his card scanner to a D-Ark. In Digimon Tamers - Episode 04, a Blue Card was revealed to have also caused Lee Jianliang's card scanner to transform. The Blue Card was later used by the Tamers to trigger the Matrix Evolution to Perfect in their partner Digimon. A Blue Card is the replacement of a Digi-Gnome in the Real World
A plastic Blue Card is packaged with some versions of both the toy D-Ark and its North American and Bandai Asia counterpart, the D-Power.