This Practice Note examines net contribution clauses (sometimes known as proportional or proportionate liability clauses) and their inclusion in collateral warranties, third party rights memoranda and consultants’ appointments. It looks at why consultants, some contractors, and their professional indemnity insurers frequently request that a net contribution clause be included in collateral warranties, third party rights memoranda and appointments and why employers are reluctant to accept them. It also considers the ability to claim a contribution from others under the Civil Liability (Contribution) Act 1978 in the absence of a net contribution clause and looks at case law regarding the effectiveness and enforceability of net contribution clauses. For suggested written advice to send to clients on net contribution clauses, see also Precedents: Advice to clients—Net Contribution clauses and Civil Liability (Contribution) Act 1978 clause. What is a net contribution clause? In modern construction projects, there are often numerous parties who are engaged to input into the design. In the event that the design is subsequently found to be defective, this can create difficulties in attributing