Horse flies and deer flies (family Tabanidae) are familiar to most Canadians, both for the persistence and painful bites of the blood-sucking females, and for the distinctive appearance of the large, often colorful adults. Horse flies and deer flies are much better known than most insects in Canada, in no small part because of the excellent account of all Canadian species in Teskey’s (1990) “The Horse Flies and Deer Flies of Canada and Alaska”. In the introduction to that volume, he describes it as “the first modern attempt to fulfill the requirements for identifying all the currently recognized species of Tabanidae of Canada and Alaska, and to plot collection records of these species, thus giving an indication of their distribution”. We feel it is time to re-address the “requirements for identifying … species of Tabanidae”, and not just because Teskey’s book is out of print and difficult to obtain. More importantly, Tabanidae lend themselves to identification using a range of colour and structural characters that were not practical to include in Teskey (1990) but that are ideal for treatment in a digital key copiously illustrated with colour photographs. We therefore here initiate a series of new guides to tabanid identification taking full advantage of newly available tools for the capture and dissemination of digital images. The present contribution is a key to the Canadian Chrysopsinae and Pangoniinae, east of the Rocky Mountains. A key to the eastern Canadian species of the third subfamily, the Tabaninae, will follow as a separate publication. These keys are to females only, since male Tabanidae are not commonly encountered. Males are keyed in Teskey (1990), however the key to males is considerably less reliable than the key to females.Distribution maps herein are based on the maps in Teskey (1990), with the addition of post-1990 records from the University of Guelph Insect Collection (Department of Environmental Biology; DEBU), from the senior authors’ personal collection (AWT), and from some post-1990 papers including Hurlburt et al. (2008) and Butt et al. (2008).