## TL;DR

SDLC is the structured process for planning, creating, testing, and deploying software. Phases: Planning → Requirements → Design → Implementation → Testing → Deployment → Maintenance. Models: Waterfall (sequential), Agile (iterative), DevOps (continuous). SDLC reduces risk, manages complexity, and ensures quality.

## Core Explanation

Waterfall: phases in strict order, no going back — works for well-understood, stable requirements. Agile: iterative sprints (1-4 weeks), continuous feedback — works for evolving requirements. DevOps: extends Agile to operations, CI/CD pipelines automate build-test-deploy. Hybrid: Wagile (Waterfall for planning, Agile for execution).

## Further Reading

- [Software Engineering (10th Ed, Sommerville)](undefined)