Thomas Merton wrote more than 70 books, mostly on spirituality, as well as scores of essays and reviews. Merton was a keen proponent of interfaith understanding.

Interest in his work contributed to a rise in spiritual exploration beginning in the 1960s and 1970s in the US. Merton's letters and diaries, reveal the intensity with which their author focused on social justice issues, including the civil rights movement and proliferation of nuclear arms. He had prohibited their publication for 25 years after his death. Publication raised new interest in Merton's life.