The Evaluation of the Impact of Natural Monopolies on the National Economy and Competitiveness provides an original approach and develops an original model for analyzing and evaluating the impact of energy market liberalization on competitiveness of Lithuania. The main scientific objective of this monograph is to develop a model for the assessment of impact of natural monopolies on competitiveness and apply this model in the energy sector. It is the hope of the author to define the best measures for mitigating negative impacts of monopolies in the energy sector. The structure of the monograph is determined by its objectives and consists of four chapters. Chapter One is dedicated to setting the theoretical background and explain the relationship between natural monopolies and countries' competitiveness, analyzing concept, features of natural monopolies and reasons for their regulation, as well as its relation to economic subjects in the country. Chapter Two presents the broad review of the Lithuanian energy sector and natural monopolies in electricity, natural gas and district heat sectors; it discusses their liberalization processes and stages of market opening. Chapter Three analyses and systematizes results of studies dealing with the impacts of the energy market opening on energy prices and competiveness. Chapter Four presents the model for multi-criteria assessments of the impact of energy market liberalization on competitiveness of Lithuania and its empirical testing on the Lithuanian power sector.