Psathyrella (Agaricales) is world-wide in distribution, occurring in tropical as well as subalpine and arctic regions. It is common to find Psathyrella on logs so rotten that they are ready to crumble or have crumbled into a shapeless mass. However, they can also be found on wood in various stages of decay or on the dead remains of both monocots and dicots, such as piles of leaves, compost piles, accumulations of herbaceous stems, etc. This treatment includes keys, descriptions, and black and white illustrations, and is an important step in understanding the Psathyrella of North American on which future researchers can build. The author cautions that much more sampling needs to be done, and, by his estimate, the completeness of the present work is that it will fall between 50 and 75 per cent of the total flora.