•An elaborate overview on the contents and tools of the BRENDA enzyme database.•BRENDA combines manually curated enzyme data with proteomic and genomic information.•The BRENDA web interfaces provides versatile tools to access enzyme information.•In 30 years BRENDA was developed from a database to a competence center for enzyme-related information. Enzymes, representing the largest and by far most complex group of proteins, play an essential role in all processes of life, including metabolism, gene expression, cell division, the immune system, and others. Their function, also connected to most diseases or stress control makes them interesting targets for research and applications in biotechnology, medical treatments, or diagnosis. Their functional parameters and other properties are collected, integrated, and made available to the scientific community in the BRaunschweig ENzyme DAtabase (BRENDA). In the last 30 years BRENDA has developed into one of the most highly used biological databases worldwide. The data contents, the process of data acquisition, data integration and control, the ways to access the data, and visualizations provided by the website are described and discussed.