In this paper, our current understanding of calorimetry is discussed, in view of the challenges offered by future applications in experiments at the LHC and the ILC/CLIC. Calorimetry is likely to become an even more crucial component of the detector complex than in the present generation of experiments. And the demands on performance will increase, in particular concerning the detection of fragmenting quarks and gluons. The (underlying reasons for the) obstacles one faces in trying to meet these demands are discussed in some detail, emphasizing the difficulties encountered in calibrating a longitudinally segmented calorimeter system. Generic R&D efforts that are being carried out in this context are described, and recent results of these projects are presented.