  We perform a systematic analysis of wrapping interactions for a general class
of theories with color degrees of freedom, including N=4 SYM. Wrapping
interactions arise in the genus expansion of the 2-point function of composite
operators as finite size effects that start to appear at a certain order in the
coupling constant at which the range of the interaction is equal to the length
of the operators. We analyze in detail the relevant genus expansions, and
introduce a strategy to single out the wrapping contributions, based on adding
spectator fields. We use a toy model to demonstrate our procedure, performing
all computations explicitly. Although completely general, our treatment should
be particularly useful for applications to the recent problem of wrapping
contributions in some checks of the AdS/CFT correspondence.
