Quality improvement is understood by Juran to be the systematic pursuit of improvement opportunities in production processes. Several methodologies are proposed in literature for quality improvement projects. Three of these methodologies – Taguchi's methods, the Shainin system and the Six Sigma programme – are compared. The comparison is facilitated by a methodological framework for quality improvement. The methodological weaknesses and strong points of each strategy are highlighted. The analysis shows that the Shainin system focuses mainly on the identification of the root cause of problems. Both Taguchi's methods and the Six Sigma programme exploit statistical modelling techniques. The Six Sigma programme is the most complete strategy of the three.