Abstract: Evolution hypothesis predicts that alien species may experience genetic changes in introduced ranges, facilitating adaptation to new habitats and range expansion. Responses to the selection pressures incurred by the novel abiotic and biotic factors in introduced ranges are primary causes for alien species evolution, although other factors such as intra- and inter-specific hybridizations, genetic shifts can also cause evolution. In this paper, we mainly analyze how alien plant species evolutionarily adapt to environmental changes related to different latitudes and altitudes, and to enemy release in introduced ranges. With respect to evolutionary adaptation to abiotic environments, we introduce some important common garden experiments and reciprocal transplant experiments, emphasizing the necessity to integrate the studies on evolution of phenotypic traits with those on neutral molecular makers. With respect to evolutionary adaptation to enemy release, we mainly discuss evolution of increased competitive ability (EICA) hypothesis, the refinement of EICA hypothesis, and their weaknesses in theory and practices. Finally, we introduce the hypothesis of the evolution of nitrogen allocation, which predicts that invasive plants may decrease leaf nitrogen allocations to defenses but increase allocations to photosynthesis in response to enemy release in introduced ranges.