  In order to achieve luminosities significantly higher than in existing
machines, future storage-ring based colliders will need to operate in novel
parameter regimes combining ultra-low emittance, large Piwinski angle and high
bunch charge; implementation of techniques such as a "crab waist" will add
further challenges. Understanding the beam-beam interaction in these situations
will be essential for the design of future very high luminosity colliders.
Recent developments in modeling tools for studying beam-beam effects, capable
of investigating the relevant regimes, will be discussed and examples,
including tests with crab waist collisions in DAFNE, will be presented.
