Unit hydrograph has long been used as a tool in flood estimation. Conventional unit hydrograph methods like the Snyder and Clark unit hydrograph models have been widely used as the model parameters are easily obtained through calibrations using computer software. For simplicity in deriving the ordinates of the unit hydrograph, methods using statistical functions to transmute unit hydrograph into probability distributions have become popular in recent years. These also include the development of synthetic unit hydrographs using empirical formulas derived from probability distributions and the characteristics of the unit hydrograph. This book presents the derivation of unit hydrograph using conventional and probability distribution methods with the aid of computer software such as Excel GRG solver, Genetic algorithm, HEC -HMS.