The defending champion in the singles Milos Raonic did not participate in the tournament again. Kei Nishikori won his third title of the year and the tenth of his career after winning tournaments in Newport and Barcelona . In the final he prevailed against John Isner 4: 6, 6: 4, 6: 4, who was in his 20th final. In doubles, Jean-Julien Rojer and Horia Tecău were successful in the previous year, they did not participate again. In the final, Bob and Mike Bryan beat Ivan Dodig and Marcelo Melo 6: 4, 6: 2. They won their 108th joint title.
The field of participants in the single competition consisted of 48 players, that of the doubles competition consisted of 16 pairs. The 16 top seeded players each received a bye into the second round. The total prize pool was $ 1,508,815; total financial liabilities were $ 1,753,020.
The qualification for the Citi Open 2015 took place on August 1st and 2nd, 2015. Six qualifiers were played in singles and a pairing in doubles, which entitle them to participate in the main field. There was also a lucky loser in singles and doubles.
At the Citi Open 2015, the following prize money and world ranking points were paid out or credited for reaching the respective round. Players who entered the main field from qualification received the specified qualification points in addition to those for reaching the respective round. Otherwise the amounts are not to be understood as cumulative. The amounts for the double competition apply to each team.