Isaac Kaufmann Funk (September 10, 1839 – April 4, 1912) was an American Lutheran minister, editor, lexicographer, publisher, and spelling reformer.

[3][6] In 1872, Funk resigned from the ministry and made an extensive tour through Europe, northern Africa, and Asia Minor.

Funk & Company, with the help of a Wittenberg classmate, Adam Willis Wagnalls, a lawyer and accountant.

In 1890 Funk published The Literary Digest, a departure from the religious works earlier in his career.

Funk was a believer in spiritualism and in his book, The Widow's Mite and Other Psychic Phenomena, published in 1904, he defended a number of mediums and spirit photography.

Magician Joseph Rinn has noted that Funk was easily duped by fraudulent mediums, such as the Bangs Sisters.