The first Doors Open Day (La Journée Portes Ouvertes) took place in France in 1984. The idea soon spread to neighbouring countries, including the Netherlands, Sweden, the Republic of Ireland, Belgium and Scotland. In 1991, these events were united as European Heritage Days at the initiative of the Council of Europe. In 2003, all 48 signatory states of the European Cultural Convention participated in European Heritage Days.

In 2000, the City of Toronto launched the first Doors Open event in North America. In 2002, the Ontario Heritage Trust launched Doors Open Ontario, the first province-wide event of its kind in Canada. The Doors Open concept continues to spread across North America with events now being held in Newfoundland, Alberta, Massachusetts, Western New York State, New York City and Denver.

Every year, Doors Open Ontario attracts large crowds across Ontario. From April to October, residents and visitors are invited to discover first-hand Ontario’s hidden heritage treasures, some of which have never been open to the public.

Since the program was launched in 2002, nearly 2.5 million visits have been made to heritage sites participating in this exciting initiative. Doors Open Ontario, now considered a cultural phenomenon, will be even larger in 2008 with hundreds of communities participating in over 40 events across the province.

Festivals and Events Ontario recognized Doors Open Ontario as one of the province's "Top 50 Ontario Festivals" in 2004 and 2005. Doors Open Ontario was nominated as a Top 50 festival in 2006 and 2007.