Knee pain is one of the most common reasons for medical consultation for musculoskeletal problems in the paediatric population. The aetiology is of very variable origin and necessitates a precise assessment. In addition to a thorough anamnesis, clinical and imaging examination methods, as well as laboratory diagnostics are of utmost importance to establish a proper diagnosis and an adequate treatment regimen. This chapter summarises the current diagnostic algorithm for dealing with knee pain in children and adolescents.