Descriptions of nearly all stages, and notes on the life histories of ten species of Rhopalosiphum Koch are offered. This includes all but two of the species known to occur in North America. Three are described as new. The group as a whole is of little economic importance with the exceptions of R. maidis (Fitch) and R. padi (L.) which are sometimes serious pests of cereal crops and have been shown to be capable of transmitting virus diseases. Keys for nearly all stages are provided.