This book introduces three new criteria (a) moment relations, (b) moment ratios and (c) ratios of the coefficients of the recurrence relations to characterize and indentify probability distributions. In general moment relations criteria are effective but there are some special situations, where the moment relations of two or more suspected distributions are same or one particular moment function takes same value for two or more distributions. In such a situation two moment ratios as extra criteria are proposed for deciding among them. This book also discussed the identification of a distribution by using the ratios of the coefficients of the recurrence relations obtained from its generating function. The significant contribution of this research is to introduce a new special class of exponential family of distributions named ‘transformed Chi-square family”. Explicit expressions for the MVUE with MV of a function of the parameter of this family are given. The critical region and the power function for various tests of hypotheses for the parameter of this family are also obtained. An identification procedure with probability of correct identification is discussed in detail.