Abstract A brief history of the investigation of fossil dinoflagellates and a summary of certain biological considerations are followed by a survey of recent progress along selected lines in the study of these organisms. Some of the new information that has come to light as a result of the reinforcing interplay between biological and paleontological investigations is reviewed and some of the nomenclatural and taxonomic questions raised by it, which will concern students of living and fossil dinoflagellates alike, are pointed out. Morphological features that distinguish theca from resting cyst and the requisite for an adequate description of the resting cyst are tabulated. An extensive bibliography includes detailed papers on the topics covered.