Code reviews have proven to be an effective means of improving overall software quality. During the review, there is an exchange of knowledge between the code author and reviewer that concerns the code being reviewed. We performed a study that looked at the code review practices of software product teams at Microsoft. The study results indicated that code reviews are a point at which design rationale is explicitly stated, but that retention and recovery of this information is not well supported in the current environment. The results also indicated that code reviews in collocated development environments such as Microsoft use a mix of face-to-face and electronic communication.