Fronts are a dynamic phenomenon separating water masses of different properties. They are narrow three-dimensional structures caused by diverse forcing mechanisms; and are characterized by distinct physical, chemical, and biological properties. Fronts occur throughout the world ocean at several spatial and temporal scales. Most stable fronts are steered by bottom topography. The most studied frontal types are tidal fronts, shelf-break fronts, upwelling fronts, estuarine fronts, plume fronts, fronts generated by convergence or divergence of water masses, frontal eddies and fronts associated with abrupt topographic features.