  Galaxy interactions/mergers, gravitational instabilities and density waves,
such as bars, are frequently invoked to trigger starbursts. These mechanisms
have been explored through numerical simulations, with the help of various star
formation recipes. Gravitational instabilities are necessary to initiate star
formation, but the main trigger might be the gas flows, to provide sufficient
fuel in a short time-scale. Gas accretion is also acting on the dynamics, in
favoring bars/spirals, which will drive the gas inwards. Large amounts of
external gas accretion are required to explain the bar frequency, and this
accretion rate can be provided by the cosmic filaments, as supported by
cosmological simulations. Subsequent interactions can then trigger starbursts
by driving this accreted gas inwards.
