This chapter is aimed at comprehensively analyzing and defining agile methodologies of software development from a software quality assurance perspective. A unique way of analyzing agile methodologies to reveal the similarities that the authors of the methods never tell you is introduced. The chapter starts by defining agile methodologies from three perspectives: a theoretical definition, a functional definition, and a contextualized definition. Then an agile quality assurance perspective is presented starting from a brief review of some of the traditional understandings of quality assurance to the innovations that agility has added to the world of quality. The presented analysis approach opens a window into an understanding of the state-of-the-art in agile methodologies and quality, and what the future could have in store for software developers. An understanding of the analysis framework for objectively analyzing and comparing agile methodologies is illustrated by applying it to three specific agile methodologies.