Crystal collects together self-adapting family of "stretch-to-fit," human-powered software development methodologies based on these understandings:
1. Every project needs a slightly different set of policies and conventions, or methodology.
2. The workings of the project are sensitive to people issues, and improve as the people issues improve, individuals get better, and their teamwork gets better.
3. Better communications and frequent deliveries reduce the need for intermediate work products.

Crystal methodologies by Alistair Cockburn