In this chapter, the importance of promoting both quality and equity in education is discussed. Specifically, it is explained that there are different views on how equity in education can be measured that are divided into two broad categories: the meritocratic and the egalitarian view. Therefore, in this introductory chapter, the main arguments supporting each of these two views are outlined. The relationships between quality and equity in education are then discussed in terms of how these are studied by researchers in the fields of psychology, sociology and economics of education. Clear definitions of the concepts of quality and equity in relation to what schools can do to promote these two dimensions of effectiveness are consequently provided, and the importance of investigating the relationships between them and comparing the effectiveness status of teachers, schools and educational systems in relation to these two dimensions is highlighted. In the last section of this chapter, the importance not only of developing theories that can explain variation in educational effectiveness in terms of quality and/or equity, but also of using these theories for improvement purposes, is discussed.