This document presents a Best Practice Manual that was developed with the existing cohort of 34 National Decade Communities to showcase the multiple ways in which National Decade Committees were established and have been operating to contribute to the Ocean Decade. It aims to highlight the achievements of existing National Decade Committees and motivate the creation of new Committees. It sets out best practice examples in relation to the development of national ocean science priorities, resource mobilization and proposes approaches for support and exchange between existing and new National Decade Committees. The attached document is also published in the IOC Ocean Decade Series under number 43.