The least that one can say about the report is that it is very enjoyable reading. Every chapter has been carefully written, and the literary merit of some chapters is outstanding (particularly those by Klemes, ‘Empirical and Causal Models in Hydrology,’ and by Baker, ‘Geology, Determinism, and Risk Assessment’). The best that one can say about the report is that it does meet its stated objectives of (1) evaluation of the adequacy of present hydrologic knowledge and of the appropriateness of present research programs to provide information for decision making and (2) description of the impact of hydrologic knowledge on the planning and management of water resources. The worst that one can say about the report is that it is not particularly original and that there are few really fresh new arguments developed in it. One notable exception is provided in Chapter 11, by Matalas, Landwehr, and Wolman, which challenges the traditional (implicit) assumption that ‘human activity is an external perturbation of the hydrologic cycle.’ Though not the explicit intent of chapter 4, by Bredehoeft, Papadopulos, and Cooper, with the explosion of the water-budget myth in groundwater, this chapter illustrates clearly the profound interaction of man (through wells) in the hydrologic cycle, a situation that cannot be comprehended from a study of the system free from human influence.