Both XP and SCRUM are derived from Agile methodology but with a slight different principle and practices. When you work in a software development team, both of the above methodologies are so close that you may get confused which one you are in. Different people provide different opinion about the differences between the two methodologies. I worked with both of the XP and Scrum team. What I learned about the differences between both of the software development approaches, I would like to share with you.
1.Scrum is a Project Management approach. But, Extreme Programming is a Software Development technique. The popular convention is that there is no 40 hour week theory in Scrum.
2.Scrum team does not allow changes during iteration (sprints). Once the project planning is over, no further change is allowed until the end of the iteration. On the other hand, XP team is much lenient about changes. If the team has not yet started on any new feature, additional feature or the modification of existing feature can be incorporated during the iteration.
3.Scrum emphasised less on engineering practices, but XP does. XP engineering practices like test driven development, automated testing, pair programming, simple design etc are very useful in terms of successful software development.
4.If I have a customer who wants to develop a software in a quick and short time, I prefer the XP.
However, if the customer is uncertain about what he wants and get more side to side communication, it is better to use the Scrum which you can also adopt some of the XP practices and principle.
5.Scrum is one component of the Agile development methodology that is associated with the daily meeting held to discuss progress and XP is a different methodology that emphasizes pair programming and test first development.
6.A key question for these methodologies are how long an iteration should be. Different people give different answers. XP suggests iterations of one or two weeks. SCRUM suggests a length of a month.
7.Some experienced project managers think that starting with Scrum has the advantages of being an easier starting point that is a little less risky. Starting with XP has the advantages of getting past some of the technical hurdles earlier.
8.Finally, Scrum is easy to adopt, very hard to master, fails silently. XP is hard to adopt, easier to master, fails noisily.