Refractories are a special class of structural ceramics and can be defined as typical non-metallic inorganic materials that constitute a unique combination of properties such as high refractoriness under high load. Classification based on the chemical nature is of prime importance since the rightful selection of a refractory for any application typically depends on the chemistry of the high temperature process environments. The failure of a refractory often occurs in metallurgical process environments due to a combined wear attack involving the most common types of mechanical, chemical, and thermal wear processes; however, the predominant wear mechanism varies with the nature of the process chemistry in distinct service atmospheres. Properties reflect the characteristic features of a refractory and unambiguously show its durability under diverse and extreme high temperature metallurgical process environments. The mechanism of refractory wear by thermal shock is illustrated for one of the most thermal shock–prone areas: the bottom portion of a basic oxygen steelmaking furnace.