Overview AAS 198th Meeting, June 2001 Session 34. Gravitational interactions and mergers are shaping and reshaping galaxies from the Local Group to the limits of the observable universe. Major mergers of nearby disk galaxies form remnants that share many properties with ellipticals and are, in essence, present-day protoellipticals. There is also growing evidence that minor mergers of companions contribute significantly to the formation of bulges in disk galaxies.
Gas plays a crucial role in such interactions.
Because of its dissipative nature, gas tends to get crunched into molecular form, turning into fuel for starbursts and active nuclei. Clearly, galaxy formation and transformation is a prolonged process occurring to the present time. In essence, the observational evidence points towards Hubble's morphological sequence being a sequence of decreasing merger damage. Research support from the National Science Foundation under grant AST-9900742 is gratefully acknowledged.