Nessus can have a number of meanings:
- Nessus (mythology), a famous centaur from Greek mythology
- The Tunic or Shirt of Nessus, the poisoned shirt of the centaur Nessus, in the story of Hercules
- Nessus, an alternate name of Nestos (god), son of Oceanus and Tethys, and god of the river Nestos
- Nessus (software), a computer security tool.
- NESSUS Probabilistic Analysis Software, a computer-based probabilistic analysis tool for assessing uncertainties in structural and mechanical systems.
- Nessus (Pierson's Puppeteer), an alien character in Larry Niven's Known Space books, of the species Pierson's Puppeteer
- 7066 Nessus, a Centaur planetoid
- Nessus, a fictional metropolis in Gene Wolfe's The Book of the New Sun, staggering in both its size and age
- Nessus, a layer of Hell in Dungeons & Dragons