Brenden Russell Aaronson (born October 22, 2000) is an American professional soccer player who plays as an attacking midfielder or winger for Premier League club Leeds United and the United States national team.

Raised in Medford, New Jersey, Aaronson attended Shawnee High School for a single year before being selected to the Philadelphia Union's YSC Academy, where he played soccer and completed his high school education. During his time at YSC Academy, Aaronson had played for Union's youth teams before committing to Indiana University and signing an amateur contract with Bethlehem Steel FC.

Aaronson appeared as an academy player playing for Bethlehem Steel FC during their 2017 season after coming through the Philadelphia Union academy. On September 30, 2017, Aaronson made his first start for Steel FC in an away draw versus Tampa Bay Rowdies. Aaronson made 21 appearances for Steel FC and scored his first goal for the professional side against Atlanta United 2.

On September 17, 2018, it was announced that Aaronson would join the Philadelphia Union at the beginning of their 2019 season. On March 17, 2019, the homegrown player scored his first professional goal in his MLS debut, helping Philadelphia tie against Atlanta United. Considered to be a back-up playmaker for the Union, injuries and suspensions gave Aaronson the opportunity to start and excel in the first team as both playmaking number 10 and left-sided box-to-box midfielder.

At the end of his rookie season, Aaronson finished second for the 2019 MLS Rookie of the Year Award, with three goals and two assists in over 1,640 minutes played. Aaronson was the youngest player out of the five finalists.

The 2020 season became a breakout year for Aaronson who finished the season with 31 appearances across all competitions and scoring 4 goals. Aaronson's performance during the season earned him several accolades include being named to the 2020 MLS Best XI for the regular season and the MLS is Back Tournament. The Union finished the season with the best league record earning the team's first trophy, the 2020 Supporters' Shield.

After persistent rumors, it was announced on October 16, 2020, that Aaronson would join Red Bull Salzburg effective January 2021 after the MLS season ended. While the transfer fee was undisclosed, Philadelphia announced that it would be the highest transfer fee paid for an American homegrown player from MLS. Early news reports indicated the fee is US$6 million up front, with US$3 million in possible incentives. Aaronson made his debut for Salzburg on January 25, as a substitute during a 2–0 victory over Rheindorf Altach.

Aaronson scored his first goal for Salzburg on February 10, 2021, scoring the game-winning goal during an eventual 3–1 win over Austria Wien. On May 1, he won his first piece of silverware with Salzburg as the club defeated LASK in the Austrian Cup final by 3–0. Aaronson scored the second goal of the match, and his fifth in all competitions since his move from Philadelphia in January.