Biological invasions—the spread of organisms following their introduction to areas outside their natural distribution as a result of human actions—are a by-product of the globalization of regional economies. Large parts of the world are currently dominated by human-modified ecosystems that often comprise a greater biomass of introduced than native organisms (Vitousek et al. 1997). The demand for an ever-increasing range of goods and services from organisms is growing worldwide, and these are, for many reasons, increasingly derived from nonnative organisms. People are designing, intentionally or by accident, ecosystems that are more productive and⁄ or congenial to them. Reasons behind the selection of the species used in building these new ecosystems are complex and change over time. Besides the obvious need for food, shelter, and other essential requirements, there is a rapidly growing trade in ornamental species, pets, and other nonessential commodities. Such demands increase the vectors (physical agents that introduce aliens) and pathways (here taken as a more complex concept, embodying the economic⁄ cultural forces that initiate and sustain the human-mediated movement of organisms between regions) for the introduction of nonnative species, and for their further dissemination within regions. These factors, acting in concert, are causing the homogenization of the world’s biota.