Understanding Scrum
Scrum is the most popular framework among Agile teams; 58% of respondents to VersionOne's 11th Annual State of Agile Report use pure Scrum. A further 10% are using a Scrum/XP hybrid.
Background
The following timeline shows a brief history of Scrum:

The first mention of Scrum in the context of product development was in The New New Product Development Game-Takeuchi, Hirotaka, and Ikujiro Nonaka, Harvard Business Review 64, no. 1 (January–February 1986).
In the paper, the two professors describe efforts by companies to try to speed up their product development life cycles to decrease their time to market. They observed that companies that were successfully doing this were employing some interesting alternative approaches.
These companies were assembling small teams of highly capable people with the right skills, setting the vision for them to build the next-generation product, giving them a budget and timeframe, and then getting out of the team's way to let it do its thing...