The sprint retrospective is usually the last thing done in a sprint. Many teams will do it immediately after the sprint review. The entire team, including both the ScrumMaster and the product owner should participate.
This one of the most overlooked ceremonies in the Scrum Process. Teams must take this time to reflect improve.
The same old retrospective will get boring to teams and will it value. Scrummando and Friends strive to innovate retrospectives and keep them fresh through our Retrospective Innovation Lab facilitated by Anthony Petrucci (@AgileSause).