Bipolar disorder is a serious mental illness, characterized by frequent recurrences and major comorbidities. Its consequences can include suicide. An S3 guideline for the treatment of bipolar disorder was developed on the basis of a systematic literature search, evaluation of the retrieved publications, and a formal consensus-finding procedure. Several thousand publications were screened, and 611 were included in the analysis, including 145 randomized controlled trials (RCT). Bipolar disorder should be diagnosed as early as possible. The most extensive evidence is available for pharmacological monotherapy; there is little evidence for combination therapy, which is nonetheless commonly given. The appropriate treatment may include long-term maintenance treatment, if indicated. The treatment of mania should begin with one of the recommended mood stabilizers or antipsychotic drugs; the number needed to treat (NNT) is 3 to 13 for three weeks of treatment with lithium or atypical antipsychotic drugs. The treatment of bipolar depression should begin with quetiapine (NNT = 5 to 7 for eight weeks of treatment), unless the patient is already under mood-stabilizing treatment that can be optimized. Further options in the treatment of bipolar depression are the recommended mood stabilizers, atypical antipsychotic drugs, and antidepressants. For maintenance treatment, lithium should be used preferentially (NNT = 14 for 12 months of treatment and 3 for 24 months of treatment), although other mood stabilizers or atypical antipsychotic drugs can be given as well. Psychotherapy (in addition to any pharmacological treatment) is recommended with the main goals of long-term stabilization, prevention of new episodes, and management of suicidality. In view of the current mental health care situation in Germany and the findings of studies from other countries, it is clear that there is a need for prompt access to need-based, complex and multimodal care structures. Patients and their families need to be adequately informed and should participate in psychiatric decision-making. Better patient care is needed to improve the course of the disease, resulting in better psychosocial function. There is a need for further high-quality clinical trials on topics relevant to routine clinical practice.