  We discuss different approaches for studying the influence of disorder in the
three-dimensional Ising model. From the theoretical point of view,
renormalisation group calculations provide quite accurate results. Experiments
carried out on crystalline mixtures of compounds lead to measurements as
accurate as three digits on the values of critical exponents. Numerically,
extensive Monte Carlo simulations then pretend to be of comparable accuracy.
Life becomes complicated when details are compared between the three
approaches.
