The Essence of Agile

According to Martin Fowler,

It's been over a decade since the developers of agile methods first started to talk about their approaches. In this time agile thinking has changed from a niche activity to an approach that is widely used. However, like any popular technique, agile software development has suffered from semantic diffusion, so much of what we see under the name of agile doesn't bear much resemblance to what the early pioneers were doing. So I think it's important to revisit the essential elements of agile thinking

I've always seen the essence of agile thinking resting on two contrasts with traditional plan-driven software engineering.

Plan-driven engineering expects us to come up with a predictive plan that precedes development. The plan lays out the people, resources and timelines for the overall project. Software design is also done up-front, with implementation expected to conform with this design. Success is measured according to how well development follows this plan. 

Agile plans are a baseline that we use to help us control change. Agile teams plan just as carefully as traditional teams, but the plans are constantly changing to reflect the things we learn during a project. Success is based on value delivered by the software.

Watch the 20-minute video of Martin Fowler explaining the history of software projects with the beginnings of plan-driven engineering (i.e., Waterfall) with agile plans.