During the last decades, the structure of the world economy has changed. Even though the market forces are still working in the same direction, nowadays we can observe some economic phenomena that were unobservable in the pure industrial economy. The thesis Theoretical Approaches to Modern Information Economy will be therefore mainly devoted to the application of classical theoretical micro- and macroeconomic concepts and relationships, especially of those whose presence is typically assumed in the modern information economy of the 21st century. Among other topics, the thesis will discuss various trends, such as low marginal costs, economies of scale both on the supply and demand side, price discrimination, tendencies to standardize, network effects, lock-in concept and the frequent complementarity of the products. Author‘s aim is to provide a synthesis of the approaches based on the recent literature, apply the theoretical approaches to discuss the real cases and to infer some of the implications for business strategy and public regulation.