Key Concepts
Agile is a mindset first — incremental delivery, customer collaboration, and embracing change over rigid planning.
Agile Manifesto
4 values + 12 principles published in 2001 that redefined how software is built.
Scrum
Time-boxed sprints (2-4 weeks), daily standups, product backlog, sprint review. Most widely used agile framework.
Extreme Programming (XP)
Technical practices: TDD, pair programming, continuous integration, refactoring, small releases.
Kanban
Visualize work on a board. Limit work-in-progress. Flow over iterations.
Concept Deep Dives
Click each concept to expand — real examples, diagrams, pros & cons.
Agile Manifesto
When to Use
Understanding the 'why' behind all agile methods.
Real-World Example
Published by 17 practitioners in 2001 as a reaction to heavyweight, document-heavy processes like RUP.
✓ Advantages
- Shifts focus to working software over documentation
- Enables fast response to change
⚠ Watch Out
- Misunderstood as 'no process' — it's actually disciplined
- Can be used to justify cutting corners
Scrum
When to Use
Team of 5-9 people. Complex product with evolving requirements. Need visibility.
Real-World Example
Spotify, Amazon, Salesforce — most tech companies run some form of Scrum or modified Scrum.
✓ Advantages
- Regular delivery rhythm
- High team visibility
- Customer feedback every sprint
⚠ Watch Out
- Doesn't scale easily to large teams without modifications
- Needs a committed, experienced Scrum Master
Extreme Programming (XP)
When to Use
Teams prioritizing code quality and technical excellence over process.
Real-World Example
Many XP practices are now standard: TDD in all serious teams, CI/CD everywhere, refactoring in all IDEs.
✓ Advantages
- High code quality
- Catches bugs early (TDD)
- Shared code ownership
⚠ Watch Out
- Pair programming = expensive (2 devs on 1 task)
- Needs a customer on-site — hard to arrange
Kanban
When to Use
Ops/support teams, continuous delivery, maintenance work without fixed sprints.
Real-World Example
GitHub Projects, Trello, Linear — all Kanban-style boards. Good for bug queues and support workflows.
✓ Advantages
- No time-boxed sprints — more flexible
- WIP limits prevent overload
- Great for ops and maintenance
⚠ Watch Out
- Less structure — can drift without discipline
- Harder to plan releases
Quick Reference
- 1Agile methods are iterative development methods designed to produce useful software quickly.
- 2Agile Manifesto (2001): 4 values + 12 principles — people over process, working software over docs.
- 3Scrum: time-boxed sprints, product backlog, daily standup. Most widely used agile framework.
- 4XP: technical practices — TDD, pair programming, CI, refactoring, small releases.
- 5Kanban: visualize work, limit WIP, optimize flow. Good for maintenance and operations.
- 6Agile scaling: large systems need elements of plan-driven approaches (SAFe, LeSS).
- 7Agile is not suitable for all projects — safety-critical systems need plan-driven approaches.
From the Book & Beyond
Case Study — The "Prescribing Medication" Story Card
Sommerville shows XP in action with a story card from the Mentcare system: Kate, a doctor, prescribes medication for a patient. The team breaks her story into task cards — change dose, formulary selection, and dose checking, a safety precaution against dangerously small or large doses. True to test-first development, "Test 4: Dose checking" is written before the code: single dose too high, too low, dose × frequency outside the safe range. One story, three XP practices — and a warning: the big weakness of user stories is completeness, because users leave things out.
2026 Perspective — Agile at 25, With AI on the Team
The Agile Manifesto turned 25 in 2026, and its values won so completely that "agile" is just how software gets built — though often as ritual Scrum rather than the XP engineering discipline this chapter describes. Two forces are reshaping it: remote-first teams replaced the shared room and physical story cards with Slack, Linear, and Jira; and AI assistants now draft code, tests, and even story breakdowns inside sprints. That makes the genuinely human parts — customer collaboration, prioritization, deciding what NOT to build — the parts that still need a standup.
Quiz — Test Yourself
Think through your answer first, then reveal.