The Delphi Technique and Nominal Group Technique are two well-recognized consensus-formation methodologies specifically designed to combine judgments from a group of experts. The Delphi Technique utilizes a series of well-defined questionnaire-based surveys, whereas Nominal Group Technique is a structured face-to-face meeting designed to facilitate consensus. Consensus-formation techniques require that each step build on the results of the previous steps. In this review, we describe these techniques, how they work, and their practical application in pediatric rheumatology, where they have been widely used to develop the outcome measures of several chronic rheumatic diseases, including juvenile idiopathic arthritis, rheumatoid arthritis, systemic lupus erythematosus, and idiopathic inflammatory myopathies, as well as the classification criteria for juvenile systemic sclerosis and juvenile vasculitides.