A clinical trial needs a carefully structured, written plan in order not only to ensure its smooth running and successful conclusion but also to gain the compulsory agreement of an ethical committee. Such a plan is called a protocol. It consists of several stages. These are: (1) An introduction; (2) A statement of aims, objectives, hypotheses and the calculation of sample size; (3) A detailed account of methodology, which itself is divided into a number of sections including the methods used in the statistical analysis of the data; (4) A study schedule and costing; (5) Any necessary appendices; and (6) A supporting bibliography. This article describes these stages in detail in the hope that a beginner can better understand the planning of a study involving members of the public.