In this chapter, the authors consider the legal duties imposed on designers and principal designers under the Construction Design and Management (CDM) Regulations: Regulation 8 – General duties, Regulation 9 – Designer duties and Regulation 11 – Principal designer duties. In addition to the general duties under Regulation 8, Regulation 9 sets out the duties that relate to all designers working on construction projects in Great Britain, including designers working overseas. The principal designer’s appointment must be in writing and made as soon as practicable before the construction phase begins, ideally at the concept design stage. Design work includes drawings, design details, specifications and bills of quantities relating to a structure, and includes calculations prepared for the purpose of a design. Regulation 12 sets out the principal designer's duties with respect to the construction phase plan and health and safety file.