Big Three (management consultancies)

The Big Three or MBB refers to management consulting firms McKinsey & Company, Boston Consulting Group, and Bain & Company. Widely considered the most prestigious strategy consulting firms in the world, 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-19th century, and strong client bases spanning some of the world's largest and more important companies.

Known for their highly selective and competitive recruiting process, the MBB firms hire a large portion of their consultants from prestigious undergraduate universities and MBA programs around the world, supplementing them with more senior industry hires with deep expertise in specific sectors served by the firms. While continuing to maintain a focus on the strategy consulting work for which they originally rose to prominence, the MBB firms have expanded their portfolio of offerings over the years to include consulting services such as operating model design, performance improvement, M&A diligence, human capital, and digital / AI transformation.

Praised by many for the impactful results they have achieved with their clients, the 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.