This volume constitutes the proceedings of the 18th International Conference on Theorem Proving in Higher Order Logics (TPHOLs 2005), which was held during 22– 25 August 2005 in Oxford, UK. TPHOLs covers all aspects of theorem proving in higher order logics as well as related topics in theorem proving and verification. There were 49 papers submitted to TPHOLs 2005 in the full research c- egory, each of which was refereed by at least three reviewers selected by the program committee. Of these submissions, 20 researchpapersand 4 proof pearls were accepted for presentation at the conference and publication in this volume. In keeping with longstanding tradition, TPHOLs 2005 also offered a venue for the presentation of work in progress, where researchers invited discussion by means of a brief introductory talk and then discussed their work at a poster session. A supplementary proceedings volume was published as a 2005 technical report of the Oxford University Computing Laboratory. The organizers are grateful to Wolfgang Paul and Andrew Pitts for agreeing to give invited talks at TPHOLs 2005.