This book reviews and summarizes the results and hypotheses raised by studies directly or indirectly dealing with the ecology of fronts and aims to identify the themes that connect them to produce a synthesis of this knowledge. Though not immediately perceived the ocean is highly structured and fronts are one of the most important components of its structural complexity. Marine fronts have been known since the early 20th Century, however, the more recent availability of high resolution satellite imagery, field measurements and numerical simulations have greatly advanced our understanding of their ecological impact. This work touches on topics such as front types, its biology and its comparisons with other bounderies at sea, as well as comparisons of fronts with terrestrial boundaries and the 'ecotone' concept. Furthermore, it also looks at the management and conservation of marine life.