Colliers International is a Canada-based global commercial real estate services organization with approximately 15,000 employees in more than 500 offices in 68 countries.

The firm provides services to commercial real estate users, owners, investors and developers; they include consulting, corporate facilities, investment services, landlord and tenant representation, project management, urban planning, property and asset management and valuation and advisory services. The organization serves the hotel, industrial, mixed-use, office, retail and residential property sectors.

The firm has headquarters in Toronto, Ontario. Annual revenues are over $2.6 billion In June 2015, it was announced that Jay S. Hennick was appointed Chairman and Chief Executive Officer and Dylan Taylor was named President and Chief Operating Officer.

Ronald Collier and Associates commenced trading in Australia in 1967 having received an appointment to carry out a strategic review of the National Australia Bank's Melbourne properties. In 1970, three separate firms commenced trading in the cities of Adelaide, Melbourne and Sydney. The eight principals involved had each known each other as former employees of Jones Lang Wootton; they traded as the Collier Group beginning September 1976. On May 18th, 1979, Colliers International Pty Ltd was registered.

In 1985, American and Canadian firms joined Colliers international, and by 1986 its Asia-Pacific operations had reached 20 markets. In 1990, the firm began to enter markets in central Europe and Latin America. In 1991 the firm Jardine Matheson purchased 50% of the Asia Pacific business and rebranded as Colliers Jardine. In 1997 Colliers Macaulay Nicolls was formed with 50% of the Asia pacific business by acquiring the shares of the original Australian shareholders.

In 2004, Colliers' parent company, FirstService Corporation, invested in Colliers Macaulay Nicolls, the predecessor of FirstService REA and the largest member of Colliers International. FirstService REA subsequently invested in several North American-based firms with operations in various commercial real estate service specialties. Among these were:

Recent geographically-based investments include:

Other expansions include:

In April 2010, Colliers and FirstService Real Estate Advisors combined their operations and global real estate services platforms, and began operation under the unified brand of Colliers International.

In June 2015, Colliers Colliers International and FirstService Corporation announced the completion of their separation into two independent, publicly traded companies – Colliers International Group Inc. and FirstService Corporation.

In October 2017, Colliers International acquired Serten Advisors, LLC; a boutique tenant representation firm headquartered in the Washington, DC area.

According to CoStar, the firm utilizes a "partnership model...- an entrepreneurial, locally-grounded company combined with the strength, reach, accountability and versatility of a global firm". FirstService REA, formed by property services firm FirstService Corp. in 2005 after buying Collier International's largest affiliate, now owns about 70% of Colliers International globally, and retains worldwide rights to the Colliers International name. The remainder of equity in Colliers is retained by local market partners."

Amid a global, industry-wide consolidation among commercial real estate brokerages, industry watchers have noted the Colliers International expansion has run counter to this trend.

According to the April 2010 issue of National Real Estate Investor (NREI), Colliers International ranked second in the magazine's annual ranking of the top twenty-five brokerages in the global real estate industry, based on its combined dollar value of leasing transactions and investment sales globally in 2009, $53.8 billion. The survey also found that Colliers International had posted an increase of more than 28 percent over its 2008 ranking, when it conducted leasing transactions and investment sales volume totaling $42 billion and ranked fifth.

In March 2010, the annual Lipsey Survey of the top 25 brands in the commercial real estate industry worldwide ranked Colliers International in the second position. The firm had held the third-place position in that survey since 2004, after rising from sixth place in 2002 to fourth in 2003.