The Software Development Life Cycle (SDLC) describes the stages a software product moves through, from first idea to eventual retirement. Understanding it helps testers see where quality activities belong — which is everywhere, not just at the end.
Classic SDLC phases
Requirements
→
Design
→
Development
→
Testing
→
Deployment
→
Maintenance
Common SDLC models
- Waterfall — sequential phases; simple but inflexible to change.
- V-Model — each development phase paired with a matching test level.
- Agile — iterative, incremental delivery with continuous testing.
- DevOps — automation-heavy, with continuous integration and delivery.
Testing belongs in every phase
Modern practice pushes quality activities as early as possible — reviewing requirements, testing designs, and automating checks that run continuously. This "shift-left" mindset means defects are caught when they are cheapest to fix.
For testers: knowing the SDLC model in use shapes your strategy. Agile needs fast, automated feedback; Waterfall needs thorough planning before a big test phase.
Conclusion
The SDLC is the backbone of how software is built. Whatever the model, testing is most effective when woven through every phase rather than bolted on at the end.