Calorimetry measures the heat generated from the early hydration reactions of cementitious materials. The heat flow tracks the rate of the overall reaction of the cementitious binder, which gives visibility into the behavior of concrete or mortar in a way that a simple set time or compressive strength test could not. The timing and shape of the temperature curve obtained through calorimetry is an indicator of relative performance of cementitious mixes, and of potential adverse interactions between materials used in the mix. In an isothermal calorimeter, the outside temperature is maintained close to constant to simulate different curing temperatures, and temperature control further allows for excellent repeatability. This paper describes some traditional, but also new applications of isothermal calorimetry in cement and concre- te technology, such as the use of isothermal calorimetry for strength prediction.