  In models of hierarchical structure formation, interactions and mergers at
high redshift play a key role in the formation and evolution of galaxies.
Numerical modeling and observations of nearby systems explore the detailed
physics of galaxy interactions, but applying these results to the high redshift
universe remains complicated. Evolution in the properties of galaxies over
cosmic history may lead to differences in interaction-induced star formation as
a function of redshift. High redshift interacting galaxies may be more prone to
extreme, disk-wide starburst activity than are low redshift systems. Also,
while activity in nearby clusters seems to be largely diminished, at higher
redshift we observe galaxies falling into clusters for the first time. A
variety of processes, including interactions and mergers, can drive strong
evolution in cluster galaxies at higher redshift.
