What is SDLC (Software Development Life Cycle)?

The Software Development Life Cycle (SDLC) is the end-to-end process for building software, from requirements through design, development, testing, deployment, and maintenance, structured into phases so teams can plan, build, and ship in a repeatable way.

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IN DEPTH

In depth.

The classic SDLC phases are requirement gathering and analysis, design, implementation (coding), testing, deployment, and maintenance. Different SDLC models arrange these differently: Waterfall runs them strictly in sequence; the V-model pairs each development phase with a matching test level; Agile runs them in short iterative cycles; and DevOps blends development and operations with continuous delivery.

For QA, the crucial point is where testing lives in the SDLC, and the modern answer is "everywhere, as early as possible." In old Waterfall projects, testing was a phase near the end, which made defects expensive to fix. Shift-left practice pulls testing activities, reviewing requirements, writing test cases, automating, into the early phases, because a defect caught in requirements costs a fraction of one caught in production.

Interviewers use the SDLC to check that you see testing as part of the whole development process, not a bolt-on. The Software Testing Life Cycle (STLC) is the testing-specific cycle that runs in parallel with the SDLC.

WHY IT MATTERS

Why interviewers ask about this.

The SDLC is foundational context for almost every process question. Showing you understand the phases, the common models, and especially where testing fits (early and throughout, not just at the end) signals process maturity.

EXAMPLE

Example scenario.

A team on a Waterfall SDLC tests only in a phase near release and keeps finding expensive, late defects. They shift to an Agile SDLC where each iteration includes test design and automation from the start, so most defects are caught within days of being written, not weeks before launch.

TIP

Interview tip.

List the phases, name a couple of models (Waterfall, V-model, Agile), and make the QA point: in modern SDLCs, testing shifts left and runs throughout, not as a final phase. Tie it to the cost of late defects.

FAQ

Frequently asked questions.

What are the phases of the SDLC?

Requirement analysis, design, implementation (coding), testing, deployment, and maintenance. Different models (Waterfall, V-model, Agile, DevOps) arrange and iterate over these phases differently.

Where does testing fit in the SDLC?

In modern SDLCs, testing fits throughout, not just before release. Shift-left practice starts testing activities (reviewing requirements, designing and automating tests) in the early phases because defects are far cheaper to fix early.