When does copyright on a book expire?

Under current US law any work created after 1978 is automatically protected for the life of the author plus 70 years. For works produced between 1964 and 1978 the term of protection is 95 years from the date of publication. If published between 1923 and 1964 and properly renewed they are also protected for 95 years from 1st publication date.

Works published before 1923 and published between 1923 nd 1964 not properly renewed are generally in the public domain.