A finite-size scaling theory for the φ 4 4 model is derived using renormalization group methods. Particular attention is paid to the partition function zeroes, in terms of which all thermodynamic observables can be expressed. While the leading scaling behaviour is identical to that of mean field theory, there exist multiplicative logarithmic corrections too. A non-perturbative test of these formulae in the form of a high precision Monte Carlo analysis reveals good quantitative agreement with the analytical predictions. * Supported by Fonds zur Förderung der Wissenschaftlichen Forschung inÖsterreich, project P7849.