Janssen Pharmaceutica is a pharmaceutical company headquartered in Beerse, Belgium. It was established in 1953 by Paul Janssen with the aim of conducting pharmacological research. The company's stated aim is the continuous development of better drugs to improve quality of life.

In 1961 Janssen Pharmaceutica was purchased by the American corporation Johnson & Johnson, and is now part of Johnson & Johnson Pharmaceutical Research and Development (J&J PRD), which conducts research and development activities related to a wide range of human medical disorders, including mental illness, neurological disorders, anaesthesia and analgesia, gastrointestinal disorders, fungal infection, allergies and cancer. Janssen and Ortho-McNeil Pharmaceutical have been placed in the Ortho-McNeil-Janssen group within Johnson & Johnson.

Janssen and its parent company have been involved in marketing fraud scandals and multi-million dollar litigation related to its antipsychotic Risperdal, accused of hiding adverse effects and bribing officials, including to promote its use among elderly patients with dementia and children with a range of conditions.