Inspired by Mao Zedong, a Chinese revolutionary leader, the rebels have fought the central government for more than four decades, demanding land and jobs for tenant farmers and the poor.
About 2,000 people - including police, rebels and civilians - have been killed in the past few years.
Maoist rebels are often called Naxalites after the Naxalbari area in eastern West Bengal state where the movement first emerged in the late 1960s.
The rebels, who have tapped into the rural poor's growing anger at being left out of the country's economic gains, are now present in 20 of the country's 28 states.
They have an estimated 10,000 to 20,000 fighters, according to India's home ministry.
Manmohan Singh, the Indian prime minister, has called them India's biggest internal security threat.