There are many quantitative studies on the behavior of consumers of new products or services. This chapter shows the starting point of three major lines of quantitative research. The next four chapters will lean heavily on these three subjects: diffusion of innovations, technology acceptance, and theory of planned behavior. The first line of research is the diffusion of innovations research that can be traced back to Rogers. One of the most important features of the book is the characterization of the persuasion step with relative advantage as a major driver for acceptation of innovations. The second line is the many applications of the technology acceptance model (TAM) that was introduced by Davis in the late 1980s. The most important result of this article is that perceived usefulness was significantly more strongly linked to usage than was ease of use, both defined in this chapter.