1920s

With the start of the 1920s Knopf began using innovative advertising techniques to draw attention to their books and authors. Beginning in 1920, Knopf produced a chapbook for the purpose of promoting new books. The Borzoi was published periodically over the years, the first being a hardback called The Borzoi and sometimes quarterly as The Borzoi Quarterly.^[9] For Floyd Dell's coming-of-age novel, Moon-Calf, they paid men to walk the streets of the financial and theatre districts dressed in artist costumes with sandwich boards. The placards had a copy of the book for browsing and directed interested buyers to local book shops.^[10]

The unique look of their books along with their expertise in advertising their authors drew Willa Cather to leave her previous publisher Houghton Mifflin to join Alfred A. Knopf.^[11] As she was still under contract for her novels, the Knopfs suggested publishing a collection of her short stories, Youth and the Bright Medusa, in 1920.^[11] Cather was pleased with the results and the advertisement of the book in The New Republic and would go on to publish sixteen books with Knopf, including their first Pulitzer Prize winner, One of Ours.^[11]

Before they had married, Alfred had promised Blanche that they would be equal partners in the publishing company, but it was clear by the company's fifth anniversary that this was not to be the case. Knopf published a celebratory fifth-anniversary book in which Alfred was the focus of anecdotes by authors and Blanche's name was only mentioned once to note that "Mrs. Knopf" had found a manuscript. This despite ample evidence from authors and others that Blanche was in fact the soul of the company. This was covered extensively in The Lady with the Borzoi by Laura Claridge.^[1]

In 1923, Knopf also started publishing periodicals, beginning with The American Mercury, founded by H. L. Mencken and George Jean Nathan, which it published through 1934.^[12]

Also in 1923, Knopf published Kahlil Gibran's The Prophet. Knopf had published Gibran's earlier works which had disappointing sales. In its first year, The Prophet only sold 1,159 copies. It would double sales the next year and keep doubling becoming one of the firm's most successful books. In 1965 the book sold 240,000 copies.^[13] Approaching its 100 year anniversary in 2023, The Prophet has been translated into over 100 languages and has never gone out of print for Knopf.

In the 1920s, Knopf sometimes withdrew or censored their books when threatened by John Sumner, such as Floyd Dell's Janet March or George Egerton's 1899 translation of Hunger.^[14][15][16]

1930s

Samuel Knopf died in 1932. William A. Koshland joined the company in 1934, and worked with the firm for more than fifty years, rising to take the positions of president and chairman of the board. Blanche became president in 1957 when Alfred became chairman of the board, and worked steadily for the firm until her death in 1966. Alfred Knopf retired in 1972, becoming chairman emeritus of the firm until his death in 1984. Alfred Knopf also had a summer home in Purchase, New York.

1940s

Following the Good Neighbor policy, Blanche Knopf visited South America in 1942, so the firm could start producing texts from there. She was one of the first publishers to visit Europe after World War II. Her trips, and those of other editors, brought in new writers from Europe, South America, and Asia. Alfred traveled to Brazil in 1961, which spurred a corresponding interest on his part in South America. Penn Publishing Company was acquired in 1943. The Knopfs' son, Alfred "Pat" Jr., was hired on as secretary and trade books manager after the war.

1950s

In 1957, editor Judith Jones joined Knopf.^[17] Jones, who had discovered Anne Frank: Diary of a Young Girl while working at Doubleday, acquired Julia Child's Mastering the Art of French Cooking for Knopf.^[18] Jones would remain with Knopf, retiring in 2011 as a senior editor and vice-president after a career that included working with John Updike and Anne Tyler.^[18]

Pat Knopf left his parents' publishing company in 1959 to launch his own, Atheneum Publishers, with two other partners.^[19] The story made the front page of The New York Times.^[19][20]

In a 1957 advertisement in The Atlantic Monthly, Alfred A. Knopf published the Borzoi Credo. The credo includes a list of what Knopf's beliefs for publishing including the statement that he never published an unworthy book. Among a list of beliefs listed is the final one—"I believe that magazines, movies, television, and radio will never replace good books."^[21]