This volume aims to address the question of what terminology planning entails in Europe. The definitions provided by ISO (ISO 29383:2020) and by the UNESCO Guidelines for terminology policies (UNESCO 2005) confirm the multifaceted nature of terminology planning. However, its implementation depends on assumptions and objectives that vary across language communities, among other factors. Unlike the definition of language planning, the ISO definition of terminology planning does not refer to the concept of language communities but instead focuses on differences among fields of knowledge or fields of application (e.g. corporate, organizational). Nonetheless, on an empirical basis, the concepts of language communities, language itself, and countries proved to be necessary for defining terminology planning and therefore useful variables for organizing the volume.