Abstract: A time and temperature integrating device for providing a visually observable indication of cumulative thermal exposure is disclosed comprising (a) at least two thermally sensitive image-forming areas of differing thermal sensitivity, and (b) indicating indicia in association with the thermally sensitive areas for indicating when each thermally sensitive area of the device has been exposed to predetermined cumulative thermal exposures. Such cumulative time-temperature exposure indicators may advantageously monitor and provide an ongoing record of thermal exposure prior to reaching a state of complete degradation, or other monitored property change, in an associated product.