Agile software development methodologies have been drawing the attention of software professionals for past few years. Agile software development methodologies follow iterative and incremental approaches to address the changing needs of customers. One of the well known agile software development method is eXtreme Programming (XP) and is derived by the sets of values-simplicity, communication, feedback and courage. The extreme practices, variation in composition and interaction between values and the feedback in XP have made the software system more complex and demands the improvement and evaluation framework to understand and evaluate XP practices in a practical way. The major aims of this book are to improve some to the extreme practices through agile modeling and evaluate the XP projects using XP evaluation framework.