Millwall Football Club have been a member of BASIS since 2021.
In January 2022, the Club launched its Environment & Sustainability strategy, Lion Living which details the approach the club has taken to date and its objectives around becoming carbon neutral.
The club operates a lion living committee, comprised of staff from around the club, including academy, training and Millwall Community Trust. In addition the club is a signatory on the UN Sport for Climate Action Framework, with the initial goal to reduce GHG emissions by 50% by 2030. The club is also a member of the EFL Green Clubs, and is a signatory to the EFL sustainable travel charter.