Large-scale lopsided asymmetry is a common phenomenon in the disk of spiral galaxies as seen in the stellar distribution as well as in the distribution of atomic hydrogen gas. Various theoretical explanations have been put forward towards explaining the physical origin of the lopsided mass distribution in spiral galaxies. Some of the yet unresolved issues are: Are these lopsided features long-lived? Why are so many isolated galaxies lopsided? In this talk, I will present a self-consistent global analysis of the lopsided perturbation in the disk and show that typical galactic disks are capable of supporting slowly varying discrete global lopsided modes. The resulting lopsided behavior closely matches with the typical observational properties. At the end I will also show the results from the N-body simulations performed to test the spontaneous growth of lopsidedness in the disk.