PAS 91 is a pre-qualification system used by UK public sector clients to assess the core capabilities of bidding contractors. It consists of a set of common questions in Annex A that assess areas like financial stability, health and safety, and business practices. Annex B includes additional optional questions. Buyer-specific questions are also asked. The 2011/12 revision aligned PAS 91 with the Government Construction Strategy, and it became mandatory for government projects in 2016.