When two galaxies approach each other, we can witness the effects of the tidal forces on a gigantic scale. Peculiar features like galactic bridges and galactic tails may form, or the two galaxies may even merge into each other and form a single system. Merger of two spiral galaxies leads to the formation of an elliptical galaxy. The interaction of gas during such galaxy encounters triggers star formation and activity of the nucleus. It is generally being accepted that galaxy interactions and mergers play a vital role in galactic evolution.