Jordan M. Zimmermann (born May 23, 1986) is an American former professional baseball pitcher. He played in Major League Baseball (MLB) for the Washington Nationals, Detroit Tigers, and Milwaukee Brewers. Zimmermann was a two-time MLB All-Star, and co-led the National League in wins in 2013. In 2014, Zimmermann pitched the first no-hitter in Washington Nationals history.

Zimmermann was born in Auburndale, Wisconsin, where he played all four years of high school on the varsity team at Auburndale High School. He began his career as a catcher, then moved to multiple positions due to his versatility. He was used as a starting pitcher as well as a closer in tight games. Zimmermann attended the University of Wisconsin-Stevens Point and played summer league baseball for the Eau Claire Express of the Northwoods League.

He was drafted by the Washington Nationals in the second round of the 2007 Major League Baseball draft as a compensation pick from the Chicago Cubs for the signing of Alfonso Soriano.

In 2008, Zimmermann had a combined 10–3 record with a 2.89 earned run average (ERA) with the Potomac Nationals of the Class A-Advanced Carolina League and the Harrisburg Senators of the Class AA Eastern League, and in July was named to the Eastern League All-Star team. He finished the season leading the organization in wins, strikeouts, and earned run average, and was the MILB.com Nationals pitcher of the year.

Zimmermann was rated the Nationals' best prospect going into the 2009 season, according to Baseball America. In 2009, Zimmermann made the Nationals' roster as the fifth starter; however, the Nationals did not need him in the rotation until mid-April, so Zimmermann opened the season with the Triple-A Syracuse Chiefs. Zimmermann's contract was purchased on April 20, 2009, and he made his major league debut that night, after a two-plus hour rain delay, against the Atlanta Braves. He pitched six innings, allowing two runs on six hits, with three strikeouts and a walk, earning the victory.

In his second game against the New York Mets, Zimmermann won his second game in as many starts, becoming the first Nationals/Expos pitcher to win his first two starts of his career since Randy Johnson did so in 1988. Coincidentally, Zimmermann was the losing pitcher in Johnson's historic 300th win on June 4, 2009.

Zimmermann experienced elbow pain, and in July landed on the disabled list. After attempted rehab, in August 2009 Zimmermann was diagnosed with a torn ulnar collateral ligament and underwent Tommy John surgery, expecting to miss 18 months. He finished his rookie season of 2009 going 3–5 with a 4.63 ERA in 16 starts.

In 2010, he made quick progress. Over four minor league levels, he started 10 games in limited play, racking up just 39+2⁄3 innings, but compiling a solid record: 1.59 ERA, 27 hits allowed, 31 strikeouts, and just six walks. On August 26, he was recalled to make his 2010 debut back in the big leagues, where Zimmermann got a no-decision in an eventual win by the Nationals over the Cardinals. On this same day, the Nationals learned that their other young pitching phenom, Stephen Strasburg, would need Tommy John surgery and would be out for 12–18 months. In Zimmermann's second return start, however, five days later, he pitched six shutout innings, allowing only one hit, no walks, and striking out nine, a personal best. He also became the first National to get through six innings facing only 18 batters. Zimmermann finished the 2010 year 1–2 with a 4.94 ERA in seven starts.