The Big Three or MBB refers to management consulting firms McKinsey & Company, Boston Consulting Group, and Bain & Company. The three companies are distinguished by the depth and rigor of their analyses and recommendations, rich histories of service dating back to their foundings in the mid-20th century, and strong client bases spanning some of the world's largest and more important companies.
The MBB firms recruit consultants from universities, MBA programs and industry. While historically associated with strategy consulting, they also provide services in areas such as operating model design, performance improvement, mergers and acquisitions due diligence, human capital and digital transformation.
MBB firms have also been the subject of criticism over the years for alleged unethical activities, with a prominent example being McKinsey's role in helping Purdue Pharma "turbo-charge" its sales of OxyContin, which has been cited as a direct contributor to the opioid epidemic in the United States.
The firms McKinsey & Company, Boston Consulting Group, and Bain & Company, collectively referred to as "MBB", are widely considered the three top and most prestigious strategy consulting firms in the world. Jobs at these firms are among the most sought after by MBA students and have a less than 1% acceptance rate.
These three firms are among the world's largest strategy consulting firms by revenue. Their latest publicly available data is summarized in the table below:
Firm Employees (year) Revenue (year) Revenue per Employee Locations (cities) Headquarters McKinsey & Company 38,000 (2025) $16 B (2025) $421 K 133 New York Boston Consulting Group 33,500 (2025) $14.4 B (2025) $429 K 100+Boston Bain & Company 18,385 (2025) $9.8 B (2025) $533 K 65Boston
See also Big Four accounting firms Corporate services List of management consulting firms
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