[en] Using an environmentally friendly renormalization group we derive an ab initio universal scaling form for the equation of state for the O(N) model, y = f(x), that exhibits all required analyticity properties in the limits x → 0, x → ∞ and x → -1. Unlike current methodologies based on a phenomenological scaling ansatz the scaling function is derived solely from the underlying Landau-Ginzburg-Wilson Hamiltonian and depends only on the three Wilson functions γ_λ, γ_ψ and γ_φ² which exhibit a non-trivial crossover between the Wilson-Fisher fixed point and the strong coupling fixed point associated with the Goldstone modes on the coexistence curve. We give explicit results for N = 2, 3 and 4 to one-loop order and compare with known results