This article analyzes diversity as related to different types of multilingual education and to sustainable development. It discusses the 'Continua of Multilingual Education', an instrument to class and collate various types of multilingual schools worldwide, as a more proper means to address diversity in multilingual education than traditional typologies. The benefits of the new tool are demonstrated by applying it to the case study of multilingual education in the Spanish Basque Country, involving the use of Basque, Spanish, English and sometimes French.