  This lecture reviews the fundamental physical processes involved in star
formation in galaxy interactions and mergers. Interactions and mergers often
drive intense starbursts, but the link between interstellar gas physics, large
scale interactions, and active star formation is complex and not fully
understood yet. Two processes can drive starbursts: radial inflows of gas can
fuel nuclear starbursts, triggered gas turbulence and fragmentation can drive
more extended starbursts in massive star clusters with high fractions of dense
gas. Both modes are certainly required to account for the observed properties
of starbursting mergers. A particular consequence is that star formation
scaling laws are not universal, but vary from quiescent disks to starbursting
mergers. High-resolution hydrodynamic simulations are used to illustrate the
lectures.
