On June 9, 1978, Canada opened its second international stamp exhibition, CAPEX ’78 (CAnadian Philatelic EXhibition). The first time had been in 1951.
The exhibition was held to mark the 100th anniversary of Canada joining the Universal Postal Union (UPU). The UPU was established in 1874 to make sending international mail easier. Canada joined the organization on July 1, 1878.
The exhibition was sponsored by the Royal Philatelic Society of Canada and was the largest and most significant philatelic exhibition in the country up to that time. In preparation of the exhibition, Canada prepared its first souvenir sheet, with a stamp-on-stamp theme. The stamps pictured imperforate pairs of three classic Canada stamps. The 14¢ first-class stamp reproduced a pair of 10-penny blue Jacque Cartier stamps first issued in December 1854. The 30¢ stamp for overseas mail reproduced the ½ penny rose Queen Victoria issue of 1857. The $1.25 stamp covering the basic registration fee pictures a pair of the H.R.H. Albert, Prince Consort stamps from 1851. A fourth stamp, not part of the souvenir sheet, reproduced a pair of 12¢ Queen Victoria stamps from 1851.
CAPEX ’78 ran until June 18. Canada would go on to hold more international exhibitions, also called CAPEX, in 1987 and 1996.