This modules introduces the concept of Fault Detection and Diagnosis in buildings (FDD) and HVAC systems. A significant amount of energy is wasted in buildings due to unnoticed faults. This could be address by embedding FDD in BMS systems (condition-based maintenance). FDD techniques (FDIDP, also including Fault Identification and Fault Prognosis) are a mature field in industries such as automotive and aeronautics. We focus on the developments of FDD science to Heating, Ventilation, Air Conditioning and Refrigeration (HVAC-R) in Buildings. A classical taxonomy proposed by Srinivas Katipamula & Michael R. Brambley is described. Examples of FDD used in different projects within the IRUSE group illustrate the pros and cons of FDD and further avenues for research.