This Operational Services and Environment Definition (OSED) document provides the basis for assessing and establishing operational, safety, performance and interoperability requirements for the Automatic Take-Off and Landing (ATOL) capability of Remotely Piloted Aircraft Systems (RPAS), requirements further detailed in the associated complementary documents: Interoperability (INTEROP) and Safety and Performance Requirements (SPR) documents. This chapter introduces the ATOL concept, illustrates the organization of the information to describe the concept and lists the inputs used as reference baseline.