Agile Software Development: Process, Manifesto, Life Cycle and Scrum Explained

Updated September 2026 · Written and maintained by the Progression Agency strategy team

Agile software development is an iterative way of building software in short cycles, releasing working increments and changing course based on feedback. This guide explains the Agile Manifesto, the agile software development process and life cycle, Scrum and Kanban, lean principles, and how agile compares with waterfall — plainly, with the terms defined.

What is agile software development?

Agile software development is an approach to building software in which cross-functional teams deliver working increments in short, repeated cycles and adapt the plan based on feedback, rather than defining everything up front and delivering once at the end.

The Manifesto for Agile Software Development

Published in 2001 by seventeen software practitioners, the Agile Manifesto sets out four values and twelve principles. The values prefer the items on the left while recognizing value in those on the right.

What is the agile software development process?

The agile process runs in cycles: maintain a prioritized backlog, plan a sprint, build and test, hold short daily standups, demo the working increment in a review, reflect in a retrospective, release, and repeat.

The agile software development life cycle

The agile SDLC repeats concept, iteration (design, build, test), release, maintenance and feedback continuously, rather than moving once through requirements, design, build, test and deploy as in waterfall.

Scrum, Kanban and other agile frameworks

Scrum

Fixed-length sprints with three roles — product owner, Scrum Master and developers — and events for planning, daily coordination, review and retrospective. See the Scrum Guide.

Kanban

A continuous flow of work visualized on a board with limits on work in progress; no fixed sprints.

Extreme Programming (XP)

Engineering practices such as test-driven development, pair programming and continuous integration.

Lean software development

Principles from lean manufacturing applied to software: eliminate waste, build quality in, deliver fast, defer commitment and optimize the whole.

Agile vs waterfall software development

Waterfall moves through fixed phases once and delivers at the end; agile delivers working software every sprint and adjusts. Agile reduces the risk of building the wrong thing; waterfall offers more up-front predictability when requirements are fixed.

Security in the agile software development life cycle

Security is built into each sprint rather than tested at the end: threat modeling during design, code review and automated scanning on every change, and penetration testing before major releases. The NIST Secure Software Development Framework describes these practices.

Agile and the MVP

In agile, the minimum viable product is the first increment released to real users; later sprints iterate on what they do.

How Progression Agency uses agile

Our software and app development projects run in two-week sprints with a written first-release scope, an installable or deployable build at the end of every sprint, and a shared backlog you can see and reprioritize.

Scrum roles, events and artifacts

The 2020 Scrum Guide defines three accountabilities, five events and three artifacts.

Scrum vs Kanban

Both are agile. Scrum works in fixed Sprints; Kanban manages a continuous flow of work with limits on work in progress.

Agile vs waterfall at a glance

Waterfall completes each phase before the next begins; agile repeats all phases in short cycles.

Agile software development cycles, user stories and testing

Agile software development cycles are the sprints: each starts with planning, ends with a review and a retrospective, and delivers working software. Work is described as agile user stories (who, what, why), the project plan is a prioritized backlog with a release roadmap rather than a fixed Gantt chart, and testing happens inside every cycle through automated tests written with the code. For how agile compares with the other software development life cycle models, see the software development life cycle.

Frequently asked questions