The substantially revised second edition of xp-explained-first-edition, co-written by kent-beck and cynthia-andres, published in 2004 three years after the agile-manifesto. The revision reflects both the intervening conversation with the broader Agile community and kent-beck's own evolution in thinking about extreme-programming.
Key differences from the first edition
The second edition made XP less prescriptive in several significant ways:
1. Expanded scope: Where the first edition was explicitly for small teams, the second edition explicitly claims applicability to any-size team.
2. Restructured framework: The second edition reorganized XP around 5 core values (adding "respect" to the original four of communication, simplicity, feedback, and courage), 11 principles, and a two-tier practice structure: 13 "primary practices" and 11 "corollary practices."
3. Primary vs. corollary practices: The two-tier structure replaced the "all-or-nothing" stance of the first edition. Primary practices are things teams can adopt independently for immediate benefit. Corollary practices build on primary practices and are harder to adopt in isolation.
4. Removed or modified practices: The metaphor practice was significantly downplayed. The "40-hour week" became sustainable-pace framing. Some practices from the first edition were removed entirely.
5. Less prescriptive stance: The "non-negotiable set of rules" framing was dropped. The second edition presents XP as a set of values and practices from which teams can build.
Intellectual contribution
The second edition's restructuring around values → principles → practices is important for understanding how kent-beck framed the relationship between the abstract and the concrete. The principle layer, largely absent from the first edition, provides a middle level of abstraction between values (why) and practices (what).
cynthia-andres's co-authorship reflects the collaborative nature of the revision and expanded the book's accessibility for non-technical audiences.
Relationship to the movement
By 2004, scrum was emerging as the dominant Agile framework, and many XP practices were being adopted outside of the full XP context. The second edition's structure accommodates this piecemeal adoption while still articulating a coherent whole. It remains the definitive statement of XP philosophy.
Key practices discussed include test-driven-development, pair-programming, continuous-integration, refactoring, collective-code-ownership, and daily-standup.