The aim of this chapter is to explain the concepts that are present when implementing a series of Content and Language Integrated Learning (CLIL) units guided based on a dynamic bilingual education in a state school. These concepts are considered necessary when it is wanted to develop proficiency in a foreign language and, at the same time, through the lessons to teach content subjects. Firstly, it is relevant to explain the term Content and Language Integrated Learning (CLIL), which according to Frigols and Marsh (2008) is a dual-focus educational approach intrinsically integrated, where the topic or subject, and the language attempt to develop a special approach in the teaching process, in which the content subject is not taught in a target language but through it (Eurydice 2006:8). Secondly, it is proper to mention a first concept related to CLIL which is bilingualism. This concept has been defined by several authors based on different perspectives and components to reach bilingualism. This has caused discussion among scholars when trying to give a definition to the term. For this reason, bilingualism will be defined according to the contribution postulated by Baker (2006), Diebold (1964), and Garcia (2009), where the explanation goes from the language proficiency, passing through social and individual issues.