This book is a collection of articles written by the two authors on the topic of equality of opportunity. All articles build on the idea that a just society should equalize the resources that determine the opportunities agents face in order to follow their goals. Resources are either external, like financial resources, or internal, like preferences or skills. The authors propose to define "equality of opportunity" as the combination of ethical principles of compensation and responsibility. The principle of compensation requires external resources to be used to compensate low-skilled agents (considering that inequalities due to skill differences are unjust). The principle of responsibility requires external resources to be allocated without regards to inequalities due to differences in preferences (considering that these inequalities are not unjust). The articles present different ways of combining the two principles in different economic contexts. The book offers many possible aspects of the analysis of equality of opportunity, ranging from axiomatic discussions in abstract compensation models, to the design of redistribution policies in concrete labor income taxation models.