The collection includes the original notebook diaries (in Polish), hundreds of letters, and personal documents and photographs, relating mainly to communism. Kowalski began keeping a diary in secondary school in Poland. In it he recorded his reactions to developments in his private life, with observations on major developments on the national and international scene. Kowalski continued to write his diary through much of his life, though his notes from the 1950s are most extensive and interesting as a source on Polish society, education and culture during the early years of the communist regime. The diary also provides a record of the author's gradual intellectual de-Sovietization and the search for his own identity. Kowalski's reactions to the death of Stalin, the revelations of the Twentieth Congress of the Soviet Communist Party, the Hungarian revolution, and the Polish October 1956 are important landmarks in the young scholar's personal liberation, a process that was very private and took decades to complete. As a university professor and a scientist, he concentrated on his teaching and research and did not reveal his complete political metamorphosis until he retired from academia in 2004. Since that time, he has written two books: Hell on Earth: Brutality and Violence under the Stalinist Regime (2008) and Tyranny to Freedom: Diary of a Former Stalinist (2009). Both books were published by Wasteland Press in Shelbyville, Kentucky.