Building information models (BIMs) make it possible to share structured data in the planning and building process and during the live cycle of the building. The models can be enrichened with information in all stages from planning to end-of-life. Predefined information requirements, data structures, and file formats allow the model to be used for design, cost planning, and time scheduling as well as analysis of building performance, and ideally also for facilities management. This chapter describes the possibilities of using application programming interfaces (APIs) to enhance the usefulness of BIM models. This provides the user with the possibility of creating own applications with real time bidirectional data exchange. Of particular interest is the exchange of data with web-based data sources. The applicability is illustrated with examples of environmental analysis based on web-based data and the use of web-based forms to enrichen BIM models with data input from building users.