Detecting and monitoring biological processes with isothermal calorimetry has been shown to be an accurate analytical technique and is proportional to the rate at which a given chemical or physical process takes place. The development of modern isothermal microcalorimeters has made the measurements of sub-microwatt amounts of heat flow possible accurate and reproducible. As a result, as few as 10,000–100,000 active bacterial cells in an individual sample are sufficient to produce a real-time signal dynamically related to the number of cells present and their activity. Specimens containing bacteria need little preparation, and isothermal microcalorimetry (IMC) is a nondestructive method. After IMC measurements, the undisturbed samples can be evaluated by any other means desired. In this webinar, a basic description of microcalorimetry and examples of microbiological applications of IMC for pathogen detection, drug susceptibility testing and ongoing research will be discussed. IMC has been used to quantify microbial activity over periods of hours or even days. Finally, the recent development of highly parallel instruments (up to 48 channels) and the constantly decreasing costs of equipment have made IMC increasingly attractive for microbiology.