Abstract. Online dictionaries rely increasingly on their users and leverage methods for facilitating user contributions at basically any step of the lexicographic process. In this paper, we propose a novel classification of the different types of user contributions, which have not been systematically studied so far. With the help of many practical examples, we discuss three major types of user contributions and discuss multiple forms and implementations of them: (i) Direct user contributions which comprise dictionary articles entirely or partly written by users in a collaborative effort. (ii) Indirect user contributions which occur in different forms of explicit feedback (e.g., by e-mail or web forms) and implicit feedback through log file analysis or external user-generated content. (iii) Accessory user contributions which go beyond the dictionary content by initiating an exchange either between the dictionary makers and their users or among the users themselves. We argue that the ease of communication and collaboration between dictionary makers and users has enormous potential, not only for keeping the dictionary up to date and at a high level of quality, but also for developing improved, user-adapted views of and access to the contents of a dictionary. Studying the different types of user contribution is crucial for effectively planning online dictionaries and for future research on electronic lexicography.