The knockout phase of the 2009–10 UEFA Champions League began on 16 February and concluded on 22 May 2010 with the final won by Internazionale against Bayern Munich 2–0 at the Santiago Bernabéu Stadium in Madrid. The knockout phase involves the sixteen teams who finished in the top two in each of their groups in the group stage.
Each tie in the knockout phase, apart from the final, was played over two legs, with each team playing one leg at home. The team that has the higher aggregate score over the two legs progresses to the next round. In the event that aggregate scores finish level, the team that scored more goals away from home over the two legs progresses. If away goals are also equal, 30 minutes of extra time are played. If there are goals scored during extra time and the aggregate score is still level, the visiting team qualifies by virtue of more away goals scored. If no goals are scored during extra time, there is a penalty shootout after extra time.
In the draw for the round of 16, matches are played between the winner of one group and the runner-up of a different group. The only restriction on the drawing of teams in the round of 16 is that the teams must not be from the same national association or have played in the same group in the group stages. From the quarter-finals onwards, these restrictions do not apply.
In the final, the tie is played over just one leg at a neutral venue. If scores are level at the end of normal time in the final, extra time is played, followed by penalties if scores remain tied.
The draw for the competition's round of 16 was held on 18 December 2009. The first legs of the round of 16 were played on 16, 17, 23 and 24 February, and the second legs were played on 9, 10, 16 and 17 March 2010.