This is an informal, preliminary proceedings of ITRS 2018: 9th Workshop on Intersection Types and Related Systems held on July 8, 2018 in Oxford, in affiliation with FLOC 2018. A formal proceedings is planned to be published after the workshop in Electronic Proceedings in Theoretical Computer Science (EPTCS).

In response to the call-for-papers, we received 6 submissions. Each submission was reviewed by 2 program committee members, and the committee decided to accept 6 papers. The program also includes 3 invited talks by Delia Kesner (joint talk with DCM), Pawel Parys and Damiano Mazza (joint talk with DCM). Their abstracts are also included in the proceedings.

We wish to thank all the invited speakers and the authors of contributed papers. We would also like to thank the program committee members for their hard work in the evaluation process, and the steering committee members for numerous advice on the organization of the workshop.

We are also grateful to the organizers of FLOC for their support in the organization of the workshop. Thanks also to the EasyChair team for providing the conference management system.