All changes to Launchpad need to be reviewed and approved by a reviewer. Most changes should have that reviewer be someone other than the author of the change. Changes made by a reviewer who is confident that the risk of the change being harmful is less than the cost of having it reviewed may be landed without a second reviewers feedback. Our goal is for every Launchpad developer to also be a reviewer, and to that end we have a mentoring process to initiate new developers onto the review team. Every "mentat" (new reviewer) is assigned a mentor (experienced reviewer) to help guide them through the process. Mentats do the reviews and the mentor reviews the mentat's review. When the mentor and review team lead agree that the mentat is ready to leave the nest, the mentat is graduated and becomes a full-fledged reviewer.
The list of reviewers and their on-call schedule is ReviewerSchedule.
Here are resources we've established to help reviewers:
We have on-demand reviewer meetings on a public IRC channel. One meeting is for Antipodeans, and the other is for Europeans and Americans.