  In this paper we study existence and orbital stability for solitary waves of
the nonlinear Klein-Gordon equation. The energy of these solutions travels as a
localized packet, hence they are a particular type of solitons. In particular
we are interested in sufficient conditions on the potential for the existence
of solitons. Our proof is based on the study of the ratio energy/charge of a
function, which turns out to be a useful approach for many field equations.
