Collective migration is a type of cell movement wherein groups of cells move together as a coherent unit. Collective migration is involved in multiple aspects of development across many organisms. Different forms of collective migration are observed in many biological processes such as gastrulation, tubulogenesis, neural crest migration and wound healing. Cancer cells can also spread via collective migration in the form of cellular streams. The hallmark of collective migration is the action of cellular mechanisms that control and shape the motility of the individual cells in the group. Despite the broad impact on normal development and disease, the molecular mechanisms that facilitate collective migration are still not well understood. I used border cell migration in the Drosophila ovary to study the mechanisms that promote collective movement. Border cell migration occurs in the egg chamber, which is composed of an oocyte and supportive nurse cells enveloped by a monolayer of follicle cell epithelium. During oogenesis, border cells originate from the follicle epithelium, assemble into a cluster of 4-6 cells and migrate in a ligand-guided fashion in between the nurse cells to reach the oocyte. Through a genetic screen, I identified new genes that are important for border cell migration. One of these genes, the serine/threonine kinase drop out (dop), promotes the stereotypic migratory behavior of the border cell cluster. Dop mutant border cell clusters extend ectopic protrusions and fail to complete migration. In vivo, collectively migrating cells maintain group cohesion while negotiating various physical hindrances such as the extracellular matrix or other cells. Border cell clusters squeeze in between larger cell types while maintaining a compact shape. I discovered waves of actomyosin contractility at the periphery of the cluster. Loss of peripheral actomyosin contractility leads to the deformation of the cluster and failure to complete migration. It is important to identify these supracellular mechanisms to understand collective migration.