Joshua Ballinger Lippincott Rosen (born February 10, 1997) is an American former professional football player who was a quarterback for four seasons in the National Football League (NFL). He played college football for the UCLA Bruins, receiving Freshman All-American and Pac-12 Freshman Offensive Player of the Year honors in 2015. As a junior, Rosen set the school's record for single-season passing yards and earned second-team all-conference honors in the Pac-12 Conference.

Rosen was selected 10th overall in the 2018 NFL draft by the Arizona Cardinals. Following an unsuccessful rookie season, he was traded to the Miami Dolphins, where he also struggled and was released after a year. Rosen spent his last two seasons as a backup for the San Francisco 49ers and Atlanta Falcons.

Rosen was born on February 10, 1997, in Torrance, California, to Charles Rosen, an orthopedic spine surgeon, and Liz Lippincott, a former journalist.

Rosen's father is Jewish and was a nationally ranked ice skater who almost qualified for the Winter Olympics in the 1970s, and his mother is a Quaker, who was the captain of the Princeton lacrosse team. Rosen had a bar mitzvah and identifies as Jewish, saying in 2016: "In retrospect, being Jewish is a big reason why I should have considered UCLA. Just because of how Jewish Hollywood is, and they really want someone to look up to because they just don't have professional athletes." As for his spiritual beliefs, Rosen describes himself as "kind of an atheist."

Rosen is the maternal great-great-great-grandson of Joseph Wharton, the co-founder of Bethlehem Steel and founder of the Wharton School at the University of Pennsylvania, which was named in his honor. Rosen is named after another ancestor, Joshua Ballinger Lippincott, who founded publishing house J. B. Lippincott & Co.

Rosen grew up playing tennis. At age 12, he was the No. 1-ranked player for his age group in Southern California, and ranked nationally in the top-50. Rosen became a top-10 player in junior rankings. He was introduced to football in elementary school by a friend's father who was a youth coach. Right before high school, Rosen switched from tennis to football.

Rosen attended St. John Bosco High School, a Catholic high school in Bellflower, California, where he had a 4.3 GPA. As a senior, Rosen was named the Los Angeles Times Player of the Year and the Long Beach Press-Telegram Dream Team Player of the Year after passing for 3,186 yards, 29 touchdowns, and four interceptions. He was named a 2014 USA Today High School All-American. Rosen was also named the Southern California Jewish Sports Hall of Fame's Male High School Athlete of the Year. During his high school career, he threw for 11,175 yards and 90 touchdowns.

Rosen was rated by both Rivals.com and Scout.com as a five-star recruit and ranked as the best quarterback in his class. Rivals also ranked him as the best overall recruit. He verbally committed to the University of California, Los Angeles (UCLA) in March 2014 before officially signing in September.