Protein is supplied by food ingredients, whole foods, sole-source foods and mixed diets and the match between dietary supply and human protein needs is vital to support the health and well-being of human populations. Since 1989 the Protein Digestibility Corrected Amino Acid Score (PDCAAS) method for evaluating protein quality has been used widely. However, limitations of PDCAAS have been recognised and new research and its application vis-à-vis other methods of estimating dietary protein quality. This report of the FAO Expert Consultation on Protein Quality Evaluation in Human Nutrition considers the effectiveness and concerns about the PDCAAS method for evaluating protein quality concerning the PDCAAS method. A new method of dietary quality evaluation called DIAAS is recommended for application in practice.