While fossil evidence supports a mid-Silurian or earlier establishment of land plants, it is clear that major diversification occurred in the Devonian. This has been summarized in several ways in recent years - the number of plant taxa (perhaps best expressed at the generic level) rapidly increases from the Early to Middle Devonian (Knoll et al., 1984; Niklas et al., 1980; Knoll, 1985); the first appearance of new structures increases through the Early and Middle Devonian and then tends to level off (Chaloner and Sheerin, 1979; Knoll et al., 1984); structural and reproductive complexity of plants increases (Chaloner and Sheerin, 1979; Edwards, 1980; Banks, 1980; Gensel and Andrews, 1984); and floral composition changes such that generalizations about plant diversity or communities can be made and seven biostratigraphic zones can be recognized (Chaloner and Sheerin, 1979; Banks, 1980). I will discuss specific aspects of these trends in the Early and Middle Devonian in this section, including consideration of biogeography and paleoecology. Vascular plants will be emphasized, but one should keep in mind that a number of non-vascular, ones also existed, some of which will be mentioned briefly. Banks' (1980) biostratigraphic zones, of which the first five are most applicable, provide a useful framework in which to discuss major events in the diversification of land plants.