  The aim of this work is to put forward a statistical mechanics theory of
social interaction, generalizing econometric discrete choice models. After
showing the formal equivalence linking econometric multinomial logit models to
equilibrium statical mechanics, a multi-population generalization of the
Curie-Weiss model for ferromagnets is considered as a starting point in
developing a model capable of describing sudden shifts in aggregate human
behaviour.
  Existence of the thermodynamic limit for the model is shown by an asymptotic
sub-additivity method and factorization of correlation functions is proved
almost everywhere. The exact solution of the model is provided in the
thermodynamical limit by finding converging upper and lower bounds for the
system's pressure, and the solution is used to prove an analytic result
regarding the number of possible equilibrium states of a two-population system.
  The work stresses the importance of linking regimes predicted by the model to
real phenomena, and to this end it proposes two possible procedures to estimate
the model's parameters starting from micro-level data. These are applied to
three case studies based on census type data: though these studies are found to
be ultimately inconclusive on an empirical level, considerations are drawn that
encourage further refinements of the chosen modelling approach.
