Deloitte, EY, KPMG, and PwC make up the Big 4 — here's how they compare

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• The Big Four — EY, Deloitte, KPMG, and PwC — are the world's largest accounting and consulting firms.
• They pull in billions annually but have faced a slowdown in demand for their services.
• This is how the Big Four have performed in recent years, and how they're looking to adapt in future.

Deloitte, EY, KPMG, and PwC are the world's largest accounting and consulting firms, known as the Big Four.

With histories dating back to the 19th century...