The aim of the study was to systematically review the hard evidence alone, concerning lithium efficacy separately for the phases and clinical facets of Bipolar disorder (BD). The PRISMA method was followed to search the MEDLINE for Randomized Controlled trials, Post-hoc analyses and Meta-analyses and review papers up to August 1st 2020, with the combination of the words ‘bipolar’, ‘manic’, ‘mania’, ‘manic depression’ and ‘manic depressive’ and ‘randomized’. Trials and meta-analyses concerning the use of lithium either as monotherapy or in combination with other agents in adults were identified concerning acute mania (Ν=64), acute bipolar depression (Ν=78), the maintenance treatment (Ν=73) and the treatment of other issues (N = 93). Treatment guidelines were also identified. Lithium is efficacious for the treatment of acute mania including concomitant psychotic symptoms. In acute bipolar depression it is efficacious only in combination with specific agents. For the maintenance phase, it is efficacious as monotherapy mainly in the prevention of manic while its efficacy for the prevention of depressive episodes is unclear. Its combinations increase its therapeutic value. It is equaly efficacious in rapid and non-rapid cycling patients, in concomitant obsessive-compulsive symptoms, alcohol and substance abuse, the neurocognitive deficit, suicidal ideation and fatigue The current systematic review provided support for the usefulness of lithium against a broad spectrum of clinical issues in Bipolar disorder. Its efficacy is comparable to that of more recently developed agents.