The process of ecological speciation has not been considered in great detail. We can gain a new perspective on this process by viewing new species as successful invaders, and by using invasive species as a model system for understanding the early stages of speciation. I propose that ecological species may be polyphyletic, and undergo genetic differentiation early in their histories. I also note that there are formidable genetic obstacles to ecological speciation. The rate of speciation is dependent on geographical and ecological variables, as are rates of invasions by exotic species. Ecological opportunity is the key for speciation and invasion; and it is most often found on young islands. In general there are no traits that presage which exotic species will be the best invaders of natural areas. Thus it would be difficult to predict which traits foster ecological speciation. Herbaceous plants are more invasive and have higher rates of diversification than woody plants.