Chapter 2 first presents terms related to crystal form, size, and shape which are used to describe what we see in thin-sections of volcanic and plutonic rocks. This is followed by definitions and illustrations of a variety of common igneous textures and how they form. Igneous rock types are presented and defined according to their mineralogy, IUGS classification, and texture, and illustrated using typical hand sample or outcrop photos. The petrogenesis and occurrence of each rock type is summarized within a plate tectonic framework, followed by representative thin-section microphotographs. Additional information is provided regarding igneous process such as nucleation and crystal growth, mineral exsolution, and magmatic zoning, as are applications related to melt generation, crystal size distribution, and anatexis.