The Agile Testing Quadrants

Introduced by B. Marick, popularized by L. Crispin and J. Gregory.

The diagram is slightly different from the book's (p. 282). The book notes that some diagrams may be different because of various context/interpretation discrepancies, or because some terms just have no well-accepted definitions.

A particular testing form may belong to more than one quadrant. For example, regression testing might fit into all quadrants.