Leonard Earl "Len" Mattiace (born October 15, 1967) is an American professional golfer on the PGA Tour.

Mattiace was born in Mineola, New York. He attended Nease High School in Ponte Vedra, Florida. He graduated from Wake Forest University in 1990 with a degree in Sociology. While at Wake Forest, he played on the team that won the NCAA Division I Golf Championship in 1986. He turned pro later in 1990.

Mattiace first gained notoriety when he surged into contention in the final round of the 1998 Players Championship. Trailing by one shot going into the par-3 17th hole, he hit his tee shot into the water, his third shot into a bunker, and his fourth shot into the water. He ended up with a quintuple-bogey 8 on the hole and finished in a tie for fifth, four strokes behind the eventual winner Justin Leonard.

Mattiace's career year was 2002, when he earned wins at the Nissan Open and the FedEx St. Jude Classic. In 2003, he contended for the The Masters Trophy by shooting a 65 in the final round which put him into a playoff with Mike Weir. On that first playoff hole, Mattiace found himself stymied by trees when his approach drifted offline. Weir needed only a bogey to secure the victory and Mattiace finished second, earning $648,000 in prize money. Shortly after the 2003 season, Mattiace's career was threatened by a skiing accident and torn ACLs in both knees.

Mattiace has been ranked in the top 50 of the Official World Golf Rankings, but has not been fully exempt on the PGA Tour since 2005. Mattiace splits his time between the PGA Tour (where he relies on past champion status for entries) and Web.com Tour. He currently resides in Jacksonville, Florida.