Depressive disorders are very common and are among the leading causes of disability worldwide. The worldwide prevalence of depression is estimated to be 4.4 per cent and prevalence in the UK is 4.5 per cent . The point prevalence of affective disorder in a large population study with intellectual disability (n=1023) was 6.6 per cent, based upon expert clinical assessment, compared with 5.7 per cent, 4.8 per cent, and 3.6 per cent for diagnoses made according to various standard criteria, respectively (Cooper et al. 2007). However, other authors have suggested higher rates of depression based on a broader criterion for a diagnosis. Depression is a common mental health problem but can be difficult to diagnose in people with intellectual disability. Antidepressants are in many areas the most widely prescribed mental health medication. The chapter presents an overview of the condition, the treatments with medication available, and their relevance.