The Database of Interacting Proteins (DIP) is an online database that integrates experimental evidence on protein–protein interactions. It aims to provide a reliable and accessible resource for researchers. The database includes information on binary protein–protein interactions and multi-protein complexes. The DIP database is implemented as a relational database using PostgreSQL. The key tables include PROTEIN, SOURCE, EVIDENCE, INTERACTION, and INT_PRT. The METHOD table provides controlled vocabulary terms and references to the PSI ontology. Information on the topology and location of molecular complexes is stored in the TOPOLOGY and LOCATION tables. The database has grown significantly, with over 18,500 distinct binary interactions and more than 2,500 referenced research articles. The database has also been enriched with information from the Protein Data Bank. Quality assessment methods have been developed to evaluate the reliability of interactions. These methods include tests based on experimental reliability and the PVM method. The DIP database provides tools for data access and exchange, including interactive and batch modes. The data are available in various formats, including XML-based XIN and tab-delimited text files. The data are also provided in the Molecular Interaction Format (MIF), a community-developed standard for protein–protein interaction data. Future directions include the development of quality assessment measures based on integration of experimental data with other sources of information. This will help in organizing and assessing the reliability of protein interaction data, and in constructing comprehensive models of protein–protein interactions. The DIP database is supported by the NIH and DOE.The Database of Interacting Proteins (DIP) is an online database that integrates experimental evidence on protein–protein interactions. It aims to provide a reliable and accessible resource for researchers. The database includes information on binary protein–protein interactions and multi-protein complexes. The DIP database is implemented as a relational database using PostgreSQL. The key tables include PROTEIN, SOURCE, EVIDENCE, INTERACTION, and INT_PRT. The METHOD table provides controlled vocabulary terms and references to the PSI ontology. Information on the topology and location of molecular complexes is stored in the TOPOLOGY and LOCATION tables. The database has grown significantly, with over 18,500 distinct binary interactions and more than 2,500 referenced research articles. The database has also been enriched with information from the Protein Data Bank. Quality assessment methods have been developed to evaluate the reliability of interactions. These methods include tests based on experimental reliability and the PVM method. The DIP database provides tools for data access and exchange, including interactive and batch modes. The data are available in various formats, including XML-based XIN and tab-delimited text files. The data are also provided in the Molecular Interaction Format (MIF), a community-developed standard for protein–protein interaction data. Future directions include the development of quality assessment measures based on integration of experimental data with other sources of information. This will help in organizing and assessing the reliability of protein interaction data, and in constructing comprehensive models of protein–protein interactions. The DIP database is supported by the NIH and DOE.