The authors propose a new approach to understand the electrostatic surface contributions to the interactions of large but finite periodic distributions of charges. They present a simple method to derive and interpret the surface contribution to any electrostatic field produced by a periodic distribution of charges. They discuss the physical and mathematical interpretations of this term. They present several examples and physical details associated with the calculation of the surface term. Finally, they provide a simple derivation of the surface contribution to the virial. This term does not disappear even if tinfoil boundary conditions are applied.