Following publication of the Conditions of Contract for Process Plants for Lump Sum Contracts in 1968, the Institute of Chemical Engineers (IChemE) in 1976 published a reimbursable form of contract known as the 'Green Book'. Second and third editions of the Green Book were published in 1992 and 2001 respectively. This Practice Note covers the 2013 (4th Edition) of the Green Book, and focuses on the nature of cost reimbursable contracts. Amendments to the Green Book were issued in February 2020 (Amendment No 1), January 2021 (Amendment No 2), and October 2025 (Amendment No 3). As with all IChemE contracts, the Green Book has detailed provisions for testing on completion and commissioning making it well suited to the process engineering industries including nuclear, water, petrochemicals, steel and food. The Green Book follows a virtually identical format to the Red Book in its clauses, layout and schedules. The drafting is very similar departing from the text of the Red Book only where necessary to reflect the implications of using a cost reimbursable