This chapter introduces the main ideas that form the basis of the agile approach. The agile approach offers a professional approach for software development that encompasses human, organizational, and technological aspects. The main ideas of agile software development were first introduced by the Agile Manifesto and later by specific agile practices that enable agile teams to accomplish their development tasks with high quality. The Agile Manifesto, formulated by seventeen software practitioners in February 2001, presents an alternative approach for software development processes compared to those used in the past 40 years. The Agile Manifesto emphasizes values such as individuals and interactions over processes and tools, working software over comprehensive documentation, customer collaboration over contract negotiation, and responding to change over following a plan. These values guide agile methods like Extreme Programming, Scrum, Lean, DSDM, Adaptive Software Development, Crystal, and others. The principle of individuals and interactions over processes and tools emphasizes the importance of people and their interactions in the development process. It suggests that efforts should focus on creating a development environment that enables participants to understand, contribute to, and collaborate with project stakeholders. The principle of working software over comprehensive documentation highlights the importance of producing quality software products, focusing on the development process and only creating necessary documents.This chapter introduces the main ideas that form the basis of the agile approach. The agile approach offers a professional approach for software development that encompasses human, organizational, and technological aspects. The main ideas of agile software development were first introduced by the Agile Manifesto and later by specific agile practices that enable agile teams to accomplish their development tasks with high quality. The Agile Manifesto, formulated by seventeen software practitioners in February 2001, presents an alternative approach for software development processes compared to those used in the past 40 years. The Agile Manifesto emphasizes values such as individuals and interactions over processes and tools, working software over comprehensive documentation, customer collaboration over contract negotiation, and responding to change over following a plan. These values guide agile methods like Extreme Programming, Scrum, Lean, DSDM, Adaptive Software Development, Crystal, and others. The principle of individuals and interactions over processes and tools emphasizes the importance of people and their interactions in the development process. It suggests that efforts should focus on creating a development environment that enables participants to understand, contribute to, and collaborate with project stakeholders. The principle of working software over comprehensive documentation highlights the importance of producing quality software products, focusing on the development process and only creating necessary documents.