Pex4Fun (http://www.pex4fun.com/) is a web-based educational gaming environment for teaching and learning programming and software engineering. Pex4Fun can be used to teach and learn programming and software engineering at many levels, from high school all the way through graduate courses. With Pex4Fun, a student edits code in any browser – with Intellisense – and Pex4Fun executes it and analyzes it in the cloud. Pex4Fun connects teachers, curriculum authors, and students in a unique social experience, tracking and streaming progress updates in real time. In particular, Pex4Fun ﬁnds interesting and unexpected input values (with Pex, an advanced test-generation tool) that help students understand what their code is actually doing. The real fun starts with coding duels where a student writes code to implement a teacher’s secret speciﬁcation (in the form of sample-solution code not visible to the student). Pex4Fun ﬁnds any discrepancies in behavior between the student’s code and the secret speciﬁcation. Such discrepancies are given as feedback to the student to guide how to ﬁx the student’s code to match the behavior of the secret speciﬁcation. This tool demonstration shows how Pex4Fun can be used in teaching and learning, such as solving coding duels, exploring course materials in feature courses, creating and teaching a course, creating and publishing coding duels, and learning advanced topics behind Pex4Fun.