Various types of composite materials are becoming an inevitable part of our day-to-day life since these are used for a variety of applications. A better understanding on the various properties of the composites is very helpful in their targeted applications, and hence characterizing the composite materials by different techniques play a major role in the development of long-life, high-quality composite products. The polymer-based composite materials provide large amount of flexibility and lightweight to the final product. The selection of various reinforcements and polymer matrices is very critical in designing a desired product. In this chapter, various techniques used for characterizing the polymer-based composite materials in order to examine their mechanical, thermal, electrical, magnetic, piezoelectric, tribological, rheological, and biological properties are discussed.