- Each team may designate up to two liberos from its list of players. A team with more than 12 players must designate two.
- Only one libero may be on court at a time (the "acting libero").
- The libero wears a uniform of a different dominant colour (or a different jacket/bib) from the rest of the team.
- Introduced in international play in the late 1990s to lengthen rallies and give smaller defensive players a role.
- Pass serve
- Dig
- Set from behind the attack line
- Replace any back-row player (unlimited)
- Serve (FIVB)
- Block or attempt to block
- Attack a ball fully above the net
- Be a front-row player