Within the Construction (Design and Management) Regulations 2015 (CDM 2015), temporary works designers (TWDs) are covered by the definition of ‘designer’ (see Paragraph 72 of the Legal Guidance, L153, Managing health and safety in construction (HSE)).The Principal Designer (PD) must ensure that all designers comply with their duties, primarily under Regulations 9 and 10.The Principal Designer has to take reasonable steps to ensure cooperation between all designers (of both permanent and temporary works), e.g. that arrangements are in place to confirm that designs are compatible.The Principal Designer’s role continues into the construction phase when design work is carried out. On a Design and Build’ (D&B) project it will be common for the D&B Contractor to be appointed as both Principal Designer and Principal Contractor.The Principal Designer should, at an early stage, discuss and agree with the Client their approach to the delivery of the role. Where the party delivering the Principal Designer role might change, this should include consideration of how any liaison and control established will be maintained.