In order to make the vision of the Barcelona Summit Agreement (mother tongue plus two additional languages) a reality through the education system, this chapter makes the case for the creation of (1) a national language policy for schools, and (2) a stakeholder-developed language policy and accompanying language planning document specifically created to meet student and teacher needs at individual school level. This chapter defines the terms ‘language policy’ and ‘language planning’, explains why language policy and language planning are so important to develop plurilingual second-level students, and delineates the dichotomies to be considered in the creation of a language policy. It emphasises the need for developing robust language planning to support language policy. The chapter then discusses the importance of devolving decision-making to schools where all stakeholders can be involved in developing the school’s language policy and planning documents. It also highlights the necessity of school-based research in the formulation of these documents and details the stages of language policy development—creation, implementation, and ongoing review. The Language Policy of the European Schools is presented as an example of a very effective document that supports the plurilingual development of its students. The chapter then discusses the research findings on language policy and planning from members of the senior leadership team in the European Schools system.