Doors Open is a celebration of community heritage. It provides residents with an opportunity to explore unique and sometimes hidden heritage treasures, some of which have never been open to the public.

The first Doors Open Day (La Journée Portes Ouvertes) took place in France in 1984. The event 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, Toronto was the first North American city to host a Doors Open event. It was quickly followed by Doors Open Ontario – the first province-wide event of its kind in Canada – with millions of people across the province visiting heritage sites since its launch in February 2002.

In its first year, Doors Open Ontario had over 40 communities participate in 17 events, attracting over 300,000 visitors to the sites. By 2003, more than 130 communities were involved.

The Doors Open concept continues to spread across North America with events now held in Newfoundland, Alberta, Massachusetts, New York State, New York City and Denver.

Markham held its first Doors Open in 2003, and since that time, Doors Open has been an annual Town-wide event. Doors Open Markham is supported by the Town of Markham, community partners and local businesses. It's a free event that draws visitors locally and from other places. The York-Durham Heritage Railway is a unique and popular feature of Doors Open Markham, highlighting the Town's railway heritage.

Doors Open Markham is traditionally held in late August, and has been either a one or two day event. Late summer is an ideal time to visit Markham's cultural heritage properties that range from the very oldest houses to the modern-era Civic Centre.

Doors Open Markham is organized under the direction of a Council-appointed committee of Town staff, municipal councillors, and community volunteers.