This Practice Note examines the approach to sub-contracting under the 1999 editions of the FIDIC Red, Yellow and Silver Books, the Gold Book 2008 and the Pink Book 2010. It also looks at the key features of the two standard form sub-contracts published by FIDIC: • Conditions of Subcontract for Construction 2011, which is for use with the Red Book 1999 and, with some amendments, the Pink Book 2010 (the Red Book sub-contract) • Conditions of Subcontract for Plant and Design-Build 2019, which is for use with the Yellow Book 1999 (the Yellow Book sub-contract) Despite being published in 2019, the Yellow Book sub-contract is for use with the 1999 edition of the Yellow Book main contract—not the 2017 edition. For information on sub-contracting under the 2017 editions of the Red, Yellow and Silver Books, see Practice Note: FIDIC contracts 2017—sub-contracting. Approach to sub-contracting in the FIDIC contracts The key principle in the FIDIC contracts in relation to sub-contracting is that the contractor remains responsible to the employer for work carried out by sub-contractors. This is enshrined