Petrology is a field of geology which focuses on the study of rocks and the conditions by which they form. There are three branches of petrology, corresponding to the three types of rocks: igneous, metamorphic, and sedimentary. The word petrology itself comes from the Greek "petros", or rock.

• Igneous petrology focuses on the genesis of rocks that crystallized from a magma.
• Metamorphic petrology focuses on the changes that a rock undergoes as a result primarily of extreme pressure and temperature.
• Sedimentary petrology focuses on the processes by which sediments, or clastics, are cemented together to form sedimentary rocks.

Petrology utilizes the classical fields of mineralogy, microscopic petrography, and chemical analyses to describe the composition and texture of rocks. Modern petrologists also include the principles of geochemistry and geophysics through the studies of geochemical trends and cycles and the use of thermodynamic data and experiments to better understand the origins of rocks.

See also Important publications in petrology