The digital economy has emerged as an integral part of the world economy. This chapter defines the concept of digital economy and provides examples illustrating the extent and versatility of this branch of economic theory. The existence of the digital economy depends entirely on the evolution of the information and communication technology (ICT) and has created some of the largest companies in the world. This technological evolution started in the 1950s and continues until today. Key evolutions include the user adoption of the Internet and mobile technologies. The academic field of digital economics has many sub-categories, such as the platform economy and the attention economy.