Essence
Agile is an umbrella of values and principles (how to think); Scrum and Kanban are concrete frameworks (how to do). The idea: short cycles, frequent feedback, willingness to change course over a year-long plan. A reaction to waterfall failures where requirements freeze at the start and go stale by the end.
Agile — 4 manifesto values
Left over right (right still has value): people & interaction > processes & tools; working product > exhaustive docs; customer collaboration > contract negotiation; responding to change > following a plan.
Scrum
Roles: Product Owner · Scrum Master · Dev Team. Artifacts: Product Backlog · Sprint Backlog · Increment. Events (timeboxed): Sprint · Planning · Daily · Review · Retrospective.
Kanban
A flow board (To Do → In Progress → Done), no mandatory sprints. WIP limit (cap concurrent work → faster flow). Flow metrics: Lead time, Cycle time, throughput.
When to use
Scrum for prioritized product development; Kanban for continuous heterogeneous flow (support, ops); often a hybrid (Scrumban).
Worked example (Kanban flow metrics)
Closed in 10 working days: 20 tasks → throughput = 2/day. Cycle time avg ≈ 2.2 days.
Little's Law: WIP = throughput × cycle time ≈ 2 × 2.2 ≈ 4.4 in progress.
Lower the WIP limit to 3 → fewer context switches → cycle time drops (~1.6d) → faster flow, same team.
Forecast: 30 queued / 2 per day ≈ 15 working days (a range).
Pitfalls
Cargo-cult rituals; "Agile = no plan/no docs"; high WIP; Daily as a boss report; Scrum where Kanban fits.