Crystal Clear is a member of the Crystal family of methodologies as described by Alistair Cockburn

Alistair Cockburn

Alistair Cockburn is one of the initiators of the agile movement in software development, helping write theManifesto for Agile Software Development in 2001 and the agile PM Declaration of Interdependence in 2005...

 and is considered an example of an agile

Agile software development

Agile software development is a group of software development methodologies based on iterative and incremental development, where requirements and solutions evolve through collaboration between self-organizing, cross-functional teams...

 or lightweight methodology

Lightweight methodology

A lightweight methodology is a software development methodology which has only a few rules and practices or ones which are easy to follow. In contrast, a complex methodology with many rules is considered a "heavyweight methodology"....

.

Crystal Clear can be applied to teams of up to 6 or 8 co-located developers

Software developer

A software developer is a person concerned with facets of the software development process. Their work includes researching, designing, developing, and testing software. A software developer may take part in design, computer programming, or software project management...

 working on systems that are not life-critical. The Crystal family of methodologies focus on efficiency and habitability as components of project safety. Crystal Clear focuses on people, not processes or artifacts.

Crystal Clear requires the following properties:

• Frequent delivery of usable code to users
• Reflective improvement
• Osmotic communication
  Communication
  Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...
  
   preferably by being co-located

Crystal Clear additionally includes these optional properties:

• Personal safety
• Focus
• Easy access to expert users
• Automated tests, configuration management
  Configuration management
  Configuration management is a field of management that focuses on establishing and maintaining consistency of a system or product's performance and its functional and physical attributes with its requirements, design, and operational information throughout its life.For information assurance, CM...
  
  , and frequent integration

Further reading

• Crystal Clear, A Human-Powered Methodology for Small Teams, Alistair Cockburn, October 2004, pages 336, paperback, Addison-Wesley Professional, ISBN 0-201-69947-8.
• Alistair Cockburn's introduction to the Crystal family of methodologies
• A quick overview with links to sample chapters from the book