The "Great Leap Forward" was Mao's attempt to rapidly industrialise China's peasant economy.
It was one of the biggest human disasters in the 20th century, as 10-40 million people died as a result of famine between 1959-1961.
The Great Leap was announced in 1958, calling for a 19% increase in steel production in that year alone, and predicting a 33% increase in industrial output - targets which are now seen as absurd.
The whole country was mobilised, so that by the end of the year 600,000 "backyard furnaces" had sprung up to make steel, often melting down useful items like cooking pots and tractors just to increase steel "production".
At the same time, the country's farmers were collectivised into 26,000 communes, each overseeing about 25,000 people and appropriating all their land.
The shake-up failed to lift food production, with disastrous consequences.
Grain output declined from 200m tonnes in 1958 to 160m tonnes in 1960, and helped to trigger the most costly famine in human history.
The Great Leap led to muted criticism of Mao. But neither he nor the Party ever apologised for the scale of the mistake.