He became active with mail art in 1980 and did several international mail art projects. From 1994 till 2001 he has conducted interviews with Fluxus and mail artists in different communication forms; the results have been published in booklets and on the internet since 1996. In later years he focused more on acrylic painting and individual correspondences. He always maintains his site with the latest details of his work.
Janssen publishes articles, magazines and booklets with his TAM-Publications and participates in international mail art projects, collaborations and exhibitions. He founded the IUOMA (International Union of Mail-Artists) in 1988 and is also the curator of the TAM-Rubberstamp Archive.
In 2003 Ruud Janssen founded together with Litsa Spathi the Fluxus Heidelberg Center.