Overview

• What you’ll learn: The Waterfall model, its strengths and weaknesses, how Agile addresses those weaknesses, and when each approach is appropriate.
• Prerequisites: Lesson 1 — What is Agile?
• Estimated reading time: 14 minutes

Introduction

Before Agile conquered the software world, there was Waterfall — the sequential, phase-based approach where requirements flow downward like water through stages: Requirements → Design → Implementation → Testing → Deployment → Maintenance. Each phase must complete before the next begins, and going back upstream is expensive.

Waterfall is not inherently evil. It works beautifully for building bridges, where requirements don’t change mid-construction. But software is not a bridge. Software requirements change constantly, users don’t know what they want until they see it, and the market shifts faster than any plan can predict.

The Waterfall Model

How It Works

Waterfall follows a strict sequence:

1. Requirements: Gather all requirements upfront. Document everything. Get sign-off.
2. Design: Create system architecture and detailed design based on the requirements.
3. Implementation: Write the code according to the design.
4. Testing: Test the completed system against the requirements.
5. Deployment: Release the finished product to users.
6. Maintenance: Fix bugs and handle change requests.

Waterfall Strengths

• Clear milestones and deliverables — easy to measure progress.
• Well-defined scope — everyone knows what’s being built.
• Works well for stable, well-understood domains (hardware, regulatory systems).
• Documentation is thorough — useful for compliance and handoffs.

Waterfall Weaknesses

• Late discovery of problems — testing happens at the end, when fixing is most expensive.
• Assumes requirements are known and stable upfront — rarely true for software.
• Customer sees the product only at the end — surprises are guaranteed.
• No room for learning — each phase is locked once completed.

The Agile Approach

Agile flips the model: instead of one long sequence, work in short iterations (typically 1-4 weeks). Each iteration delivers a potentially usable increment of the product. Requirements, design, coding, and testing happen in every iteration.

When to Use Which

• Waterfall fits: Regulated industries with fixed requirements (medical devices, aerospace), hardware manufacturing, projects where the problem and solution are well-understood.
• Agile fits: Software development, product innovation, projects with evolving requirements, competitive markets where speed matters.

Key Takeaways

• Waterfall is sequential and plan-driven; Agile is iterative and feedback-driven.
• Waterfall assumes requirements are stable; Agile assumes they will change.
• Neither approach is universally superior — the right choice depends on the domain, the project, and the level of uncertainty.
• Most modern software development benefits from Agile because requirements are rarely stable and feedback is essential.

What’s Next

In Lesson 3, you will survey the major Agile frameworks — Scrum, Kanban, XP, and SAFe — to understand which tools are available in the Agile toolkit.