In 30 seconds
- Waterfall runs phases in sequence; agile cycles through them in small loops.
- Waterfall suits fixed, well-understood work; agile suits uncertainty.
- Many real projects mix the two.
Pick Waterfall when…
- Requirements are stable and well understood
- Changes late are very expensive (construction, hardware)
- Regulation demands full upfront specification
Pick Agile when…
- Requirements will change as users react
- Early feedback reduces risk
- Delivering value in slices beats one big launch
Side by side
| Waterfall | Agile | |
|---|---|---|
| Planning | Upfront, detailed | Continuous, lightweight |
| Delivery | One release at the end | Frequent increments |
| Change | Controlled, costly | Expected, welcomed |
| Customer involvement | Start and end | Throughout |
| Risk shows up | Late | Early |
A note on history
The 1970 paper by Winston Royce usually cited as the origin of waterfall actually warned that a purely sequential process was risky and recommended iteration. The Agile Manifesto came 31 years later.
Myth vs reality
Myth · Agile is always better.
Reality · For stable, fixed-scope work, a plan-driven approach can be cheaper.
Myth · Waterfall has no feedback.
Reality · It has feedback, just later and at higher cost.
Myth · You must pick one.
Reality · Many organizations plan in phases and build in sprints.
FAQ
Is Scrum the opposite of waterfall?
Scrum is one agile framework; waterfall is a sequential lifecycle. They differ mainly in how often you deliver and replan.
Can a fixed-price contract be agile?
Yes, by fixing time and cost and letting scope flex by priority.
Why do agile projects still fail?
Usually because the rituals are adopted without the values, or the organization around the team doesn't change.