Public health practitioners and researchers often seek to influence public policies in order to improve population health and/or reduce health inequalities. However, these efforts frequently appear to be uninformed by the many empirically-based theories about policymaking that have been developed within political science. This glossary provides a brief overview of some of the most popular of these theories, describing how each: frames the policymaking process; portrays the relationships and influence of specific policy actors; and depicts the potential for policy change (or inertia). Examples of their application to public health are provided to help improve understanding of the material presented. Throughout the article, the implications of the different theories for public health researchers and advocates seeking to inform policy decisions are emphasised. The glossary aims to provide an accessible overview to key theories about policy and decision-making, with a view to supporting public health efforts to achieve healthier public policies.