"Concurrency and Nets" is a special volume in the series "Advances in Petri Nets." Prepared as a tribute to Carl Adam Petri on the occasion of his 60th birthday, it is devoted to an outstanding personality and his pioneering and fruitful scientific work. Part I (70 pages of over 600) presents the congratulatory addresses and invited talks that were given at an Anniversary Colloquium. The contributions of this part honor Carl Adam Petri and his work from many different perspectives. Part II is a collection of invited papers discussing various aspects of the theme Concurrency and Nets. These papers are contributed partly by researchers that were or are still associated with the Petri Institute at GMD and partly by researchers whose scientific work deals with Net Theory or related system models. The topics range from basic theoretical aspects to application oriented methods.