The rebels say they are fighting for the rights of poor tribal people
India's bloody Maoist insurgency began in the remote forests of the state of West Bengal in the late 1960s.
Decades later Prime Minister Manmohan Singh described it as India's "greatest internal security challenge".
Maoists are also known as "Naxalites" because of the violent left-wing uprising in 1967, which began in the West Bengal village of Naxalbari.
Although this was eventually quashed by police, over the years India's Maoists have regrouped and asserted control over vast swathes of land in central and eastern India, establishing a so-called "red corridor".
This spans the states of Jharkand, West Bengal, Orissa, Bihar, Chhattisgarh and Andhra Pradesh and also reaches into Uttar Pradesh, and Karnataka.
The Maoists and affiliated groups are thought to control more than one third of India's 600-odd districts.
And more than 6,000 people have died in the rebels' long fight for communist rule in these states.
The Maoists' military leader is Koteshwar Rao, otherwise known as Kishenji.
Thousands of rebels are said to swell his guerrilla ranks - estimates vary from 10,000 to 20,000 armed fighters. They are said to get most of their weapons by raiding police bases.
Analysts say the longevity of the Maoist rebellion is partly due to the local support they receive.
The rebels say they are fighting for the rights of indigenous tribespeople and the rural poor who they say have been neglected by governments for decades.
Maoists claim to represent local concerns over land ownership and equitable distribution of resources.
Ultimately they say they want to establish a "communist society" by overthrowing India's "semi-colonial, semi-feudal" form of rule through armed struggle.
Major rebel attacks
And over the years the Maoists have managed to launch a series of damaging attacks on Indian security forces.
In 2009, rebels gained virtual control of the Lalgarh district in West Bengal barely 250km (155 miles) from the state capital Calcutta.
For many months, rebels, supported by local villagers, held hundreds of paramilitary forces at bay. The Maoists declared it to be India's first "liberated zone" but Indian security forces finally overwhelmed the rebels.
March 2010 saw rebels ambush paramilitary troops in the dense jungles of central Chhattisgarh state, killing at least 75 soldiers. Correspondents say it was the worst-ever Maoist attack on Indian security forces.
In 2007, also in Chhattisgarh, Maoist rebels killed 55 policemen in an attack on a remote police outpost.
Almost every week, Maoist rebels are blamed for minor skirmishes and incidents across India's north-east - common tactics include blowing up railway tracks and attacking police stations.
But the Maoists are now facing India's biggest ever anti-Maoist offensive - Operation Green Hunt.
Nearly 50,000 federal paramilitary troops and tens of thousands of policemen are taking part in the operation across several states.
Rebels have vowed to intensify their attacks unless the government halts its offensive against them.
India's government in turn has pledged to crack down even harder unless rebels renounce violence and enter peace talks.
Analysts say the chances of dialogue or any kind of rapprochement are slim.
A BBC Report