Mangroves are a diverse group of predominantly tropical trees and shrubs growing in the marine intertidal zone where conditions are usually harsh, restrictive and dynamic. Here, they are subject to both shorter term rhythms of tides and seasons, as well as longer term changes of climate and sea level. As a group, they share several highly specialised and collectively well-known adaptations, notably exposed breathing roots, support roots and buttresses, salt excreting leaves, and viviparous water-dispersed propagules. However, as individuals, we know less about then, exemplified by the mistaken belief that these characters might be shared equally by all species. Therefore, it this chapter, it was necessary first to clarify and enhance the concept and definition of what is a mangrove, prior to discussing their biogeography, and why they occur in certain localities and not others. It will also be seen that the genetic diversity of thes plants belies their ecological uniformity, raising serious doubts fro ideas of shared ancestry with theit co-inhabitors. Finally, the concept of the mangrove habitat wiil be enhanced by knowing more about the individuals that provide te structural framework and trophodynamic coherence to this unique ecosystem.