This volume contains the papers presented at HOR 18: 9th Workshop on Higher-Order Rewriting held on July 7, 2018 in Oxford.

HOR is a forum to present work concerning all aspects of higher-order rewriting. The workshop aims to provide an informal and friendly setting to discuss recent work and work in progress concerning higher-order rewriting, broadly construed. This includes rewriting systems that have functional variables or bound variables, the lambda-calculus and combinatory logic being paradigmatic examples.

This is the 9th edition of HOR. The previous ones have been held in:

1. Copenhagen, Denmark (as part of FLoC 2002);
2. Aachen, Germany (as part of RDP 2004);
3. Seattle, USA (as part of FLoC 2006);
4. Paris, France (as part of RDP 2007);
5. Edinburgh, UK (as part of FLoC 2010);
6. Nogaya, Japan (as part of RTA 2012);
7. Vienna, Austria (as part of RTA-TLCA 2014);
8. Porto, Portugal (as part of FSCD 2016).