This chapter examines the following concepts: history of composite materials testing, quality control principles, component materials testing, mechanical testing, thermal and environmental testing, flammability testing, and non-destructive testing and inspection. In general, the properties of metals, ceramics, and plastics are known because of the large databases for these materials compiled over the years. The same is not true for composites. The lack of an accepted composites database is due to many factors, including the following: the complexity of composites, the relative newness of composites as materials, the continuous development of new composites, and the scarcity of standardized tests for composites. Testing can be viewed from two different perspectives. One view is a determination of the fundamental properties of the composite material. The other is to investigate the in use properties of the composite by monitoring changes in the composite’s properties over time or under various environmental conditions. This information is used to verify that a composite part has the properties expected over its useful life. Most of the tests that have been described in this chapter are destructive, that is, the sample is no longer fit for use after the test has been conducted. To gain further confidence in the integrity of the parts, several non-destructive tests (NDT) have been developed to investigate the nature of the product, including the effectiveness and reliability of the manufacturing process.