This book is an extended Goddard's case study for the inheritance of "feeble-mindedness", a general category referring to a variety of mental disabilities including intellectual disability, learning disabilities, and mental illness. He concluded that a variety of mental traits were hereditary and that society should limit reproduction by people possessing these traits. The name Kallikak is a pseudonym used as a family name throughout the book, coined from the Greek words καλός (kallos) meaning good and κακός (kakos) meaning bad. In its day, "The Kallikak Family" was a tremendous success and went through multiple printings. It helped propel Goddard to the status of one of the nation's top experts in using psychology in policy, and along with the work of Charles B. Davenport and Madison Grant is considered one of the canonical works of early 20th-century American eugenics.