Anthropogenic habitat loss and fragmentation have been implicated as among the key drivers of the burgeoning global biodiversity crisis. In response, there is a growing mandate among natural resource managers to evaluate the impacts of proposed management actions on the extent and fragmentation of habitats. Unfortunately, few guidelines exist to help managers understand the many complex issues involved in the quantitative assessment of habitat loss and fragmentation. In our Primer, we explore habitat fragmentation as a landscape-level process in which a specific habitat is progressively sub-divided into smaller, geometrically altered, and more isolated fragments as a result of both natural and human activities. We describe alternative perspectives on fragmentation in which habitat patches are viewed either as analogs of oceanic islands embedded in an ecologically neutral sea or as patches of variable quality embedded within a complex and heterogeneous mosaic of patches of varying suitability and affects on habitat connectivity. In the conventional island biogeographic perspective, habitat loss and fragmentation is described as a landscape transformation process involving several recognizable phases that are demarcated by significant changes in the pattern or function of the landscape. We describe the key spatial components of habitat loss and fragmentation: habitat extent, subdivision, geometry, isolation, and connectivity, and their affects on individual behavior and habitat use, population structure and viability, and interspecific interactions. Finally, we view the evidence, both theoretical and empirical, regarding the issue of when is habitat fragmentation important, and conclude that it depends not only on the pattern of habitat distribution but on the life history characteristics (e.g., dispersal capabilities) of the target organism(s).