Hydrology is the science through which man tries to understand the properties and the distribution of water. Frequency analysis is a set of mathematical and statistical techniques used to describe the probability of occurrence of events. Every year, floods and droughts cause loss of life and millions of dollar's worth of damage in many countries of the world. In many cases, these consequences could be reduced either by nonstructural means such as restricting building in flood plains and by limiting water abstractions, or by better design of regulatory structures to reduce flood peaks and increase low flows. In all these cases, the key is knowledge of the distribution of flows in the river. Frequency and Risk Analyses in Hydrologydescribes some of the methods currently used to apply frequency analysis techniques to hydrological data in order to provide planners and engineers with figures that they can use in practice to reduce the losses caused by flood and drought. Risk analysis is an extension of the technique used to assess the probability that the estimated design event will differ from the actual event.