We have created a Massive Open Online Course (MOOC) about dictionaries and dictionary-making, to be hosted by FutureLearn. This paper discusses the design and development of this course, which is pitched at high school and undergraduate level participants as well as language enthusiasts around the world. The MOOC will answer questions such as: how dictionaries are made and how this process has changed over time; what goes into a dictionary and who decides; and what kinds of language evidence underpin the information which dictionaries provide. Participants will be encouraged to compare the quantity and quality of information in different types of dictionary, and will investigate corpus-based and computational lexicographic methods. It will also consider dictionary users’ attitudes and common misconceptions, taking into account the requirements and habits of English language learners as well as fluent speakers. By the end of the course, participants will know about some of the latest trends in lexicographic research, the roles of language technology, corpora and crowdsourcing in the dictionary compilation process, the range of possible dictionary entry components, lexicographical choices and computational methods surrounding the selection and ordering of word meanings, and the content and wording of definitions.