Urbanization is widely recognized as a major factor promoting biological invasions worldwide. In this article, we provide insights into the patterns of biological invasions in Beijing, one of the largest and quickly urbanizing cities of the world, by developing a comprehensive list of naturalized and invasive flora and their associate traits (e.g., distribution, life form, habitat, or geographic origin). One hundred and twelve naturalized (including 48 invasive) plants have been identified within the Beijing Municipality. Most of the naturalized and invasive plants belong to four families (Asteraceae, Poaceae, Amaranthaceae, and Euphorbiaceae) and are annual herbs that preferentially grow in disturbed sites. North and South America are the main contributors to the naturalized and invasive flora of Beijing. As expected, those Beijing districts that have recently experienced the highest human population growth, urban expansion, and the largest economic growth are also those with the highest number of naturalized and invasive species. Urban expansion is predicted to continue in the near term making additional invasions likely that will significantly increase the proportion of introduced species in Beijing's flora. An integrated management strategy for the whole municipality is urgently needed that includes comprehensive scientific research that documents the extent of invasions and their effects on Beijing's economy and environment.