Trillian may refer to:
- Trillian (character), a fictional character in The Hitchhiker's Guide to the Galaxy
- Trillian (software), an instant messaging client
- Trillian (sculpture), a planned Belfast public art sculpture by Ed Carpenter, scrapped due to rising cost
- Project Trillian, an effort to port the Linux kernel to the Intel IA-64 architecture
- Trillian, a misspelling of trillion