Although Boxx was a member of the United States Under-21 national team pool, she did not receive her first senior cap until August 2003, when U.S. national team coach April Heinrichs named her to the team's 2003 FIFA Women's World Cup squad, making her the first uncapped player to be named to a U.S. Women's World Cup squad.
Prior to the call-up, following the suspension of WUSA, Boxx had planned to take a coaching position at Cal State-Dominguez Hills and pursue a graduate degree at Pepperdine University.

Boxx scored a goal in each of the two pre-World Cup friendlies, against Costa Rica and Mexico, and in the opening match of the World Cup against Sweden, Boxx became the first American woman to score three goals in her first three matches with the national team.

Boxx started five matches at the Women's World Cup, scoring again against Canada in the third place match.
She was voted the player of the match against Canada by the FIFA Technical Study Group, who said Boxx "seized control of the game, spurred on her team-mates and finally scored the decisive goal in USA's victory".

Boxx started 31 of 32 national team matches she played in 2004, including all six matches at the 2004 Olympics, where she scored a goal, assisted on another and helped the team win a Gold Medal.
She scored eight goals over the course of the year, including a hat trick against Trinidad and Tobago in an Olympic qualifying match.
Boxx came in seventh in the voting for the 2004 FIFA World Player of the Year award.

In 2005, Boxx started all nine matches US national team matches, playing all but 23 minutes of all matches played.
She was a finalist for the 2005 FIFA World Player of the Year, coming in third behind Birgit Prinz and Marta.

Boxx missed most of 2006, first for surgery to repair torn cartilage in her right hip, and then for torn medial collateral ligaments she suffered on her first day back in training with the national team.
She returned in 2007 after an eight-month layoff, and was named to the United States' squad for the 2007 FIFA Women's World Cup.
Boxx helped the team reach the semifinal match against Brazil, but she was sent off after receiving two yellow cards, and the United States went on to lose 4–0.

Boxx played every minute of all five U.S. games in the 2008 Summer Olympics in Beijing.

In 2011, she played in all but one of the World Cup games, earning defensive team honors for her efforts throughout the tournament.
 During the World Cup final against Japan, which went to overtime penalty shoot-out, Boxx was one of the Americans elected to take one of the penalty kicks, and had her shot saved by Japan's goalkeeper Ayumi Kaihori.

(*Correct as of December 15, 2012)
Although Boxx was a member of the United States Under-21 national team pool, she did not receive her first senior cap until August 2003, when U.S. national team coach April Heinrichs named her to the team's 2003 FIFA Women's World Cup squad, making her the first uncapped player to be named to a U.S. Women's World Cup squad. Prior to the call-up, following the suspension of WUSA, Boxx had planned to take a coaching position at Cal State-Dominguez Hills and pursue a graduate degree at Pepperdine University.
Boxx scored a goal in each of the two pre-World Cup friendlies, against Costa Rica and Mexico, and in the opening match of the World Cup against Sweden, Boxx became the first American woman to score three goals in her first three matches with the national team.
Boxx started five matches at the Women's World Cup, scoring again against Canada in the third place match. She was voted the player of the match against Canada by the FIFA Technical Study Group, who said Boxx "seized control of the game, spurred on her team-mates and finally scored the decisive goal in USA's victory".
Boxx started 31 of 32 national team matches she played in 2004, including all six matches at the 2004 Olympics, where she scored a goal, assisted on another and helped the team win a Gold Medal. She scored eight goals over the course of the year, including a hat trick against Trinidad and Tobago in an Olympic qualifying match. Boxx came in seventh in the voting for the 2004 FIFA World Player of the Year award.
In 2005, Boxx started all nine matches US national team matches, playing all but 23 minutes of all matches played. She was a finalist for the 2005 FIFA World Player of the Year, coming in third behind Birgit Prinz and Marta.
Boxx missed most of 2006, first for surgery to repair torn cartilage in her right hip, and then for torn medial collateral ligaments she suffered on her first day back in training with the national team. She returned in 2007 after an eight-month layoff, and was named to the United States' squad for the 2007 FIFA Women's World Cup. Boxx helped the team reach the semifinal match against Brazil, but she was sent off after receiving two yellow cards, and the United States went on to lose 4–0.
Boxx played every minute of all five U.S. games in the 2008 Summer Olympics in Beijing.
In 2011, she played in all but one of the World Cup games, earning defensive team honors for her efforts throughout the tournament.  During the World Cup final against Japan, which went to overtime penalty shoot-out, Boxx was one of the Americans elected to take one of the penalty kicks, and had her shot saved by Japan's goalkeeper Ayumi Kaihori.
(*Correct as of December 15, 2012)
Shannon Boxx