ProofWeb is both a system for teaching logic and for using proof assistants through the web. ProofWeb can be used in three ways. First, one can use the guest login, for which one does not even need to register. Secondly, a user can be a student in a logic or proof assistants course. We are hosting courses free of charge. If you are a teacher and would like to host your course on this server, send email to Thirdly, if teachers do not want to trust us with their students’ files, they can freely download the ProofWeb system and run it on a server of their own. ProofWeb works well with many web browsers, but it does not work with all versions of Internet Explorer. ProofWeb was developed using the Firefox browser, which can be downloaded for free.