This book is an introduction to the methodologies for the uncertainty analysis of atmospheric dispersion under uncertain environment. The uncertainty issues in atmospheric dispersion are generally addressed within a purely probabilistic framework. A framework may exist where the information of the parameters are epistemic in the sense of fuzzy or epistemic and aleatory combined together. There is a need for methodologies of sensitivity and uncertainty analysis of atmospheric dispersion in those frameworks. In order to address uncertainties such as fuzzy, probability and imprecise probability new methodologies are proposed and discussed through hypothetical case studies of atmospheric dispersion. Methodologies such as fuzzy-imprecise probability, hybrid stochastic response surface method and construction of probability bound through stochastic response surface methods have been developed and are discussed here.