This chapter describes the development process of the TOEFL Primary tests. It explains the intent of the TOEFL Primary tests and presents a conceptual foundation that helped define what the tests should measure. The chapter describes how the final design of the TOEFL Primary tests was made throughout the test development process. The TOEFL Primary tests are designed to accommodate a broad range of English proficiency levels represented in the intended population. The Council of Europe suggested that the proficiency levels A1, A2, and B1 on the Common European Framework of Reference (CEFR) be expected for most elementary or low secondary students learning a foreign language in the formal school environment. The chapter discusses the key points related to the language learning of young English is a foreign language (EFL) students, and describes how information from EFL curricula and textbooks informed the construct definition of English ability for the TOEFL Primary tests.