MPEJ Volume 14, No. 1, 21 pp. Received: Nov 1, 2007. Revised: May 8, 2008. Accepted: May 16, 2008. I.Gallo, P. Contucci Bipartite mean field spin systems. Existence and solution ABSTRACT: A mean field spin system consisting two interacting groups each with homogeneous interaction coefficients is introduced and studied. Existence of the thermodynamic limit is shown by an asymptotic sub-addittivity method and factorization of correlation functions is proved almost everywhere. The free energy solution of the model is obtained by upper and lower bounds and by showing that their difference vanishes for large volumes. http://www.maia.ub.es/mpej/Vol/14/1.ps http://www.maia.ub.es/mpej/Vol/14/1.pdf http://www.ma.utexas.edu/mpej/Vol/14/1.ps http://www.ma.utexas.edu/mpej/Vol/14/1.pdf http://mpej.unige.ch/mpej/Vol/14/1.ps http://mpej.unige.ch/mpej/Vol/14/1.pdf