Like resource groups, condition groups need to have criteria for their design in order to judge whether the proposed groupings are satisfactory. However, the key criterion of similarity of condition is much more difficult to define and measure. Both aspects of condition groups have been important in the developments in the USA and elsewhere. This chapter reviews a number of approaches to the issue of condition classification, and starts with general schemes, which aim to cover the whole spectrum of disease, but also covers some specialized classifications for particular types of patient. Disease staging has been used for predicting resource use, and also as a severity adjuster for comparisons of mortality rates. Patient management categories are groupings of conditions based upon patient management pathways (PMPs). The chapter also reviews way of classifying the whole spectrum of health conditions, but some of the particular approaches for specific groups could be considered.