Autism Diagnostic Interview – Revised (ADI-R) and Autism Diagnostic Observation Schedule, Second Edition (ADOS-2) are well-validated semi-structured instruments, widely used in clinical practice and research for decades. They both follow highly standardised procedures to provide a thorough assessment of individuals suspected of having autism spectrum disorder (ASD). Both instruments have been found to be useful in differentiating between children, adolescents and adults with ASD and those with non-ASD diagnoses, especially when both are used in combination. As with many measures of ASD symptoms, scores on ADI-R and ADOS-2 have been shown to be susceptible to effects of developmental variables, including age and IQ as well as behavioural difficulties of a subject. Experienced clinicians are aware that the scores can be affected by comorbidity or sex of an individual, which is the case in females with autism who have not been diagnosed early in life or those who do not have intellectual disability and/or profound communication difficulties. The article presents ADI-R and ADOS-2 in a succinct way along with basic recommendations for their use, which are the same regardless of location and country. The purpose of this article is to present guidelines and standards of use for ADI-R and ADOS-2 which are distinguished from the standards of purchase. Administration and coding of ADI-R and ADOS-2 are highly standardised, and based on these guidelines, only professionals who completed ADI-R and ADOS-2 test-specific trainings can be considered competent users to provide valid assessments.