This chapter provides a comprehensive overview of the knowledge acquisition process for built heritage, structured through multiple levels of investigation. It begins by outlining the knowledge path, followed by the identification of the building and the geometric survey, comparing traditional techniques with reality data capture technologies such as photogrammetry, terrestrial laser scanning, and UAVs. The chapter then addresses the critical-historical analysis, including documentary research, interpretation, and the study of construction phases. Detailed attention is given to building techniques and construction details, as well as to material surveys, non-destructive investigation methods (including infrared thermography, endoscopy, and ultrasound), decay analysis, crack pattern analysis and foundation conditions. The final section is dedicated to Heritage Building Information Modelling (HBIM), presenting its evolution, components, and applications in conservation, restoration, facility management, and documentation. The chapter also discusses technical challenges related to data accuracy, interoperability, and heterogeneous data management in HBIM, while outlining future directions for integrating emerging technologies and sustainable conservation practices.