The UITP workshop series provides a forum for researchers interested in discussing human interaction with logic-based systems in general, including automated deduction tools and interactive proof assistants. The workshop welcomes papers aiming at designing, developing and evaluating user interfaces for such systems.

This volume contains the proceedings of the 13th International Workshop on User Interfaces for Theorem Provers (UITP 2018), held on the 13th of July 2018 as part of Federated Logic Conference (FLoC) in Oxford, UK. Each submitted paper was reviewed by two to three referees, and following an online discussion, six research papers were selected to be published in these informal proceedings and were presented at the workshop. The program also included an invited talks given by Jamie Vicary (University of Oxford), who presented "Designing Globular: formal proofs as geometrical objects". The UITP workshop was enriched by a joint session with the Isabelle workshop.

We are grateful to the invited speaker and thankful to all participants of the UITP 2018 Workshop, especially to the authors for their submissions and to the members of the Program Committee of UITP 2018 for their professional work in the review process. We also would like to thank the Workshop Chairs and the Organizing Committee of FLoC 2018 for the smooth organization and for providing the great environment to which UITP was affiliated.