Ivan Illich was a deep thinker whose varied life and thoughts are not easy to understand or summarise. He trained as a catholic priest, but resigned the priesthood.
His knowledge of over a dozen languages helped him to carry out research in often unregarded areas to try to understand the roots of the key ideas and practices underpinning the modern world. In the 1970s he developed a radical critique of economic globalisation, at a time at which few had grasped its implications. Although growing up in Europe and moving to US, he was highly critical of Western cultural hegemony, and explored South America and Asia on foot.
He was highly critical process of institutionalisation, whereby fixed procedures and practices replaced autonomous decision making and personal connections. If they grow beyond a certain size, he believed, personal commitment and fellowship dwindles, and institutions become counter-productive, ending up by promoting the causes whey claimed to be opposing. Deschooling Society, which influenced thinkers such as John Holt and John Taylor Gatto, was his most popular book, perhaps because it was more easily understood. His critiques of medicine, work, energy use, and economic development are less understood but may be more radical.