Ophiocordyceps sinensis and Cordyceps militaris are the two best-known species in the genus Cordyceps sensu lato. Here, we review recent research progresses of these two fungi on their taxonomy, distribution, life cycle and mode of sexual reproduction, host range, genetic diversity, molecular genetics and genomics, ecology, artificial cultivation and related-product developments. We also discuss the major issues remaining in the current research for these two fungal organisms and suggest the approaches for future studies.