The Moss-PAS (Diag ID) is a semi-structured clinical diagnostic interview with separate sets of questions for patients and informants. It is primarily designed for diagnosis of mental health conditions in people with intellectual disability who have enough language to give at least some verbal contribution to an interview, but can also be used as an informant-only interview. It has been developed from the well-known PAS-ADD 10 psychiatric interview and PAS-ADD Clinical Interview, but has been completely updated and re-designed on the basis of more than twenty five years' experience of training users around the world. The Moss-PAS (Diag ID) is probably the most sophisticated patient interview that is globally available for people with intellectual disability, and for those who have limited language skills. It is also suited to research studies, and for any routine clinical assessment requiring a precise evaluation of symptoms. The interview produces criterion-by-criterion diagnoses under both ICD-11 and DSM-5.