Bipolar Disorder (BD) I and II have long been well known psychiatric diseases that can be controlled with psychopharmacological and behavioural treatment. Over the past decades its prevalence remained stable (BD I 0.6% and BD II 0.4%, worldwide). Aetiology and pathophysiology of BD remain still largely unknown, however, recent research effort, especially genetic research using Genome Wide Association Studies (GWAS) and Copy Number Variations (CNVs) methodologies in extremely large samples, has shed some light into the neurobiology. Bipolar Disorder is now considered a bridging disease belonging to both the psychotic and the mood spectrum, with different dimension differentially involved in individual patients.