This paper examines the nature of dictionaries and encyclopedias, focusing on some of the preparation that has gone into the construction of a dictionary of language testing at the University of Melbourne (Australia). It discusses the purpose of such dictionaries, the nature and size of dictionary/encyclopedia entries, and the readability of entries. It also reports on an experiment to determine the proper length and difficulty level of possible entries. Twenty-one M.A. students were asked to read three sets of entries and comment on their length, difficulty, and lexical density. It was found that there was substantial agreement among the students as to whether several entries were too long, too short, or about right, and if they were difficult, easy, or about right. An appendix contains copies of the possible dictionary entries. (MDM)