Oil and gas companies need to consider and understand the potential public health impacts of their projects and operations in order to define their responsibilities with regard to local communities and host governments. A health impact assessment (HIA) is a structured planning and decision-making process for analysing the potential positive and negative impacts of programmes, projects, and policies on public health. These can then be addressed in a timely and appropriate manner to achieve positive outcomes and cost benefits while also enhancing sustainability. This guide defines and outlines the purpose and value of health impact assessments within the oil and gas industry, and details a six-step HIA implementation process. It revises and updates the 2005 guide, and includes ‘lessons learned’ and new HIA developments. The guidance is intended as a technical resource for both subject matter experts and project staff who work on the potential health impacts of oil and gas projects.