The law on spatial planning in member states is fundamental to its practice. The terms used give insights into the way planning is understood. Law assigns powers, duties, rights and lines of accountability for spatial planning. It establishes the outline of planning instruments, procedures and for some countries, their substantive goals for planning. Legal definitions and terms used in Europe are diverse. The chapter explains that there is common attention to establishing arrangements for the regulation of physical development, and in most cases legal means to protect environmental assets. Many countries mandate sustainability and/or economic growth goals for planning in law. No two definitions are the same. Some explain planning primarily as a set of procedures whereas others say much more about what planning is intended to achieve. Some countries specify the components of planning in detail, others provide only a framework within which the specifics can change quickly.