The Clarke Irwin Paperback Series commenced publication in 1963 and had its demise in 1970. There is an argument on whether this series was a direct competitor to the NCL as most of the 38* books in the series were not books of fiction. The series did not restrict its titles to novels and short stories as the bulk of the NCL did. It published art books, autobiographies, histories, and the occasional novel and play.
But saying that it did somewhat compete with the NCL since the company did publish these books with an idea on the educational market in which the NCL concentrated back in the decades after WWII. Robertson Davies had his first publication with Clarke Irwin. Other titles such as A Gentlewoman of Upper Canada by Anne Langton brought to mind Susanna Moodie, Catherine Parr Traill and Anna Brownell Jameson.
Clarke Irwin’s biggest sales came in textbooks, but these paperbacks also made their imprint on Canadians and therefore deserve a place in The Competition section of the website.
*at present, I know of 38 titles in the series, if this increases I will make the appropriate changes.