Fifty-one years of hourly reports of cloud layers from eighty-four airport stations across Canada are used to examine trends in various types of clouds. The records required rather extensive pre-processing to account for major discontinuities in the observing procedures and quality control, to assess impacts of automation and changing archiving practices, and to classify the layers into low, middle, and high cloud categories. Annual, seasonal, day- and night-time trends in the occurrence of mainly cloudy sky conditions in the summation amounts of low, middle, and high clouds are computed, as well as trends in the occurrence of convective and stratiform clouds.