Martin James Schreiber (/ˈʃraɪbər/ SHRY-bər; born April 8, 1939) is an American politician, publisher, author, and lobbyist who served as the 38th lieutenant governor of Wisconsin from 1971 to 1977, and (following the resignation of Patrick Lucey) as the 39th governor of Wisconsin from 1977 to 1979. Schreiber has become an advocate on issues related to Alzheimer's disease and dementia.

Schreiber was born in Milwaukee, Wisconsin. His father Martin E. Schreiber was a Republican member of the Wisconsin State Assembly (1941–1944), and later a member of the Milwaukee Common Council (1944 to 1976). The younger Schreiber attended the youth government and leadership program Badger Boys State in 1956 as a representative chosen from Milwaukee Lutheran High School. He attended Valparaiso University and the University of Wisconsin–Milwaukee, where he was a member of Tau Kappa Epsilon fraternity, majoring in urban studies. He later earned a J.D. degree from Marquette University Law School in 1964.

A member of the Democratic Party, Schreiber served in the Wisconsin State Senate from 1963 to 1971. During his political career, Schreiber focused on education, children's issues, consumer protection, and the rights of workers and the elderly. Schreiber was the youngest senator in state history, having been elected at age 23.

In 1970, Schreiber was elected lieutenant governor on the Lucey-Schreiber ticket. He was elected the youngest chairperson for the National Lieutenant Governors Association in 1972.

In July 1977, following the resignation of Lucey to become the United States ambassador to Mexico, Schreiber succeeded him as Governor for the remainder of their four-year term. In the 1978 election, Schreiber faced a divisive primary challenge by developer David Carley. In the general election, political newcomer Lee S. Dreyfus, a populist Republican and skilled orator, waged an unconventional campaign and successfully attacked the Lucey-Schreiber record on taxes and big government. Schreiber lost 54% to 44%.

Following the election, Schreiber moved to Stevens Point, Wisconsin and became vice-president of Sentry Insurance. He ran for the governor's office again in 1982, campaigning against Anthony S. Earl, former head of the Wisconsin Department of Natural Resources. He did not get past the Democratic primary election and returned to Sentry Insurance.

Schreiber ran again for office in 1988, seeking the Mayoralty of Milwaukee, but was defeated by John Norquist.

In 1988, after leaving electoral politics, Schreiber formed his own public affairs consulting firm, becoming a successful lobbyist.