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, but others are in the form of essays or philosophical books. Translations of his works are difficult and multiple translated versions of his works exist.
Lem made his literary debut in 1946 as a poet, and at that time he also published several dime novels. Beginning that year, Lem's first science fiction novel Człowiek z Marsa (The Man from Mars) was serialized in the magazine Nowy Świat Przygód (New World of Adventures). Between 1947 and 1950 Lem, while continuing his work as a scientific research assistant, published poems, short stories, and scientific essays. However, during the era of Stalinism, all published works had to be directly approved by the communist regime. Lem finished a partly autobiographical novella Hospital of the Transfiguration (Szpital Przemienienia) in 1948, but it was suppressed by the authorities until 1955 when he added a sequel more acceptable to the doctrine of socialist realism. In 1951 he published his first book, Astronauci (The Astronauts); it was commissioned as juvenile SF and Lem was forced to include many references to the 'glorious future of communism' in it. He later criticized this novel (as well as several of his other early pieces, bowing to the ideological pressure) as simplistic; nonetheless its publication convinced him to become a full-time writer.