Pair Programming:

Pair programming is a software development technique in which two programmers work together at one work station. One types in code while the other reviews each line of code as it is typed in. The person typing is called the driver. The person reviewing the code is called the observer or navigator. The two programmers switch roles frequently (possibly every 30 minutes or less).
While reviewing, the observer also considers the strategic direction of the work, coming up with ideas for improvements and likely future problems to address. This frees the driver to focus all of his or her attention on the "tactical" aspects of completing the current task, using the observer as a safety net and guide.
Benefits:
· Design quality: Shorter programs, better designs, fewer bugs
· Reduced cost of development: With bugs being a particularly expensive part of software development, especially if they're caught late in the development process, the large reduction in defect rate due to pair programming can significantly reduce software development costs
· Learning and training: Knowledge passes easily between pair programmers: they share knowledge of the specifics of the system, and they pick up programming techniques from each other as they work
· Overcoming difficult problems: Pairs often find that seemingly "impossible" problems become easy or even quick, or at least possible, to solve when they work together
· Improved morale: Programmers report greater joy in their work and greater confidence that their work is correct
· Decreased management risk: Since knowledge of the system is shared among programmers, there is less risk to management if one programmer leaves the team
· Increased discipline and better time management: Programmers are less likely to skip writing unit tests, spend time web-surfing or on personal email, or other violations of discipline, when they are working with a pair partner. The pair partner "keeps them honest"
· Fewer interruptions: People are more reluctant to interrupt a pair than they are to interrupt someone working alone