This first article in a seven part series presents an overview of the essential elements of the GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach that has proved extremely useful in systematic reviews, health technology assessment reports, and clinical practice guidelines. GRADE guidance has appeared in many articles dealing with both core issues and more specialised and complex guidance, and it has evolved over time. This series of articles presents GRADE essentials, Core GRADE, focusing on the core judgments necessary to summarise the comparative evidence about alternative care options and to make recommendations that apply to the care of individual patients. This article presents detailed guidance on formulating questions using the PICO (population, intervention, comparison, outcome) structure, and refining the question considering possible differences in relative and absolute effects across patient groups. The article then provides an overview of the remainder of the Core GRADE approach, including decisions about the certainty of the evidence and considerations in moving from evidence to guidance and recommendations.