MLwiN is a statistical software package for fitting multilevel models. It uses both maximum likelihood estimation and Markov chain Monte Carlo (MCMC) methods. MLwiN is based on an earlier package, MLn, but with a graphical user interface (as well as other additional features).^[1] MLwiN represents multilevel models using mathematical notation including Greek letters and multiple subscripts, so the user needs to be (or become) familiar with such notation.

For a tutorial introduction to multilevel models and their applications in medical statistics illustrated using MLwiN, see Goldstein et al.^[2]