The Thirteenth Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Gravitation, and Relativistic Field Theory (MG13) will take place at Stockholm University in Stockholm, Sweden July 1 - 7, 2012. Preregistration will take place Sunday, July 1, 3:00 pm - 7:00 pm and the official opening of the meeting Monday morning, July 2, both at the Aula Magna lecture hall. During the six day conference a wide variety of topics will be discussed in the morning plenary sessions beginning with mathematical topics on Monday, quantum aspects of gravity on Tuesday, precision tests of general relativity on Wednesday, relativistic astrophysics on Thursday, cosmology and astroparticle physics on Friday and the latest scientific news and the history of physics Saturday. There will be five plenary lectures each morning and up to twenty parallel sessions in the four weekday afternoons excluding Wednesday, which is left free for a trip and the evening conference banquet. The plenary lectures will be held in the Aula Magna lecture hall and the parallel sessions at the AlbaNova University Center, both easily reachable by public transportation from the city center. The banquet will be held in Solliden, inside the open air museum Skansen.