In 1931, his book Eine Geschichte der Juden was published by Rowohlt Verlag in Berlin (and later translated into English, Hebrew and Dutch).
According to Douglas Reed, Kastein was a "zealous Zionist historian... who holds that the Old Testament was in fact a political programme, drafted to meet the conditions of a time, and frequently revised to meet changing conditions.... and that the Law laid down in the Old Testament must be fulfilled to the letter.
"[1] A wide range of works by Kastein were published between 1918 and 1942, including poetry, novels, and essays.
There has been a revival of interest in his writing in the twenty-first century, with his memoir Was es heißt, Jude zu sein : eine Kindheit in Bremen [What it means to be a Jew: a childhood in Bremen] published in 2004[2] and a new edition of one of his novels, Pik Adam, published in 2017.
[3] The Leo Baeck Institute holds two archival collections relating to Kastein, one in New York and one in Jerusalem.