  Using Environmentally Friendly Renormalization, we present an analytic
calculation of the series for the renormalization constants that describe the
equation of state for the $O(N)$ model in the whole critical region. The
solution of the beta-function equation, for the running coupling to order two
loops, exhibits crossover between the strong coupling fixed point, associated
with the Goldstone modes, and the Wilson-Fisher fixed point. The Wilson
functions $\gamma_\lambda$, $\gamma_\phi$ and $\gamma_{\phi^2}$, and thus the
effective critical exponents associated with renormalization of the transverse
vertex functions, also exhibit non-trivial crossover between these fixed
points.
