Collisionless may refer to:

  • In information theory and computer science, computer networking architectures where collisions between packets of data cannot occur
  • In computer science, situations where collisions, or occurrences of the same value, cannot occur in a structure (and prevent reliable lookups)
  • In cosmology and physics, a medium in which the interaction cross-section between particles is so low that collisions between particles have no significant effect on the system. See Shock waves in astrophysics.