His books have been translated into 41 languages and have sold over 27 million copies. At one point, he was the most widely read non-English-language science fiction author in the world. His works explore philosophical themes; speculation on technology, the nature of intelligence, the impossibility of mutual communication and understanding, despair about human limitations and humankind's place in the universe. They are sometimes presented as fiction, to avoid both trappings of academic life and limitations of readership and scientific style, but others are in the form of essays or philosophical books. Translations of his works are difficult; Michael Kandel's translations into English have generally been praised as capturing the spirit of the original.