The State Bank of India (SBI) is India's largest bank. It originated from three presidency banks established in 1806, 1840, and 1843, which merged in 1921 to form the Imperial Bank of India and then became the SBI in 1955 when the Reserve Bank of India acquired a controlling stake. SBI has acquired several smaller banks over the years to expand its presence across India. Today it has over 14,000 branches within India and 180 offices in 34 countries internationally, making it one of the largest banks in the world.