A contractual brief is a signed agreement that specifies the requirements and timeline for completing a project. It protects both parties by allowing legal action if the terms are not met. A formal brief outlines requirements without signatures, making it less legally binding. An informal brief has no written terms, increasing risks of unpaid work or an incomplete project. A co-operative brief involves multiple companies working together without contracts, while a negotiated brief allows compromising on conflicting ideas from an original brief.