Ceramic armor is armor used by armored vehicles and in personal armor to resist projectile penetration through its high hardness and compressive strength. In its most basic form, it consists of two primary components: A ceramic layer on the outer surface, called the "strike face," backed up by a ductile fiber reinforced plastic composite or metal layer. The role of the ceramic is to (1) fracture the projectile or deform the projectile nose upon impact, (2) erode and slow down the projectile remnant as it penetrates the shattered ceramic layer, and (3) distribute the impact load over a larger area, which can be absorbed by ductile polymer or metallic backings. Ceramics are often used where light weight is important, as they weigh less than metal alloys for a given degree of resistance. The most common materials are alumina, boron carbide, and, to a lesser extent, silicon carbide.

Tests as early as 1918 demonstrated the potential of ceramic armor; Major Neville Monroe-Hopkins found that adding a thin layer of enamel to steel greatly improved its ballistic properties. Its first operational use was not until the Vietnam war in which helicopters frequently came under small arms fire. In 1965, ceramic body armor was given to helicopter crews, and 'hard-faced composite' armor kits were added to pilot seats. By the following year, monolithic ceramic vests and airframe-mounted armor panels had been deployed. In "Huey" helicopters, these improvements were estimated to have decreased fatalities by 53%, and non-fatal injuries by 27%.

Ceramic armor designs range from monolithic plates to systems employing three dimensional matrices. One of the first patents of ceramic armor was filed in 1967 by the Goodyear Aerospace Corp. It embedded alumina ceramic spheres in thin aluminum sheets, which were layered so that the spheres of each layer would fill the gaps between spheres of the surrounding layers, in a manner similar to a body-centered cubic packing structure. The entire system was held together with polyurethane foam and either thick aluminum, multi-layered UHMWPE, para-aramid fiber, or 30% PALF + 70% epoxy composite backing. This development demonstrated the effectiveness of matrix-based design, and spurred the development of other matrix-based systems. Most of these combine cylindrical, hexagonal, or spherical ceramic elements with a backing of some non-armor dedicated alloy. Monolithic plate armor, by contrast, relies on single plates of an advanced ceramic slipped into a traditional ballistic vest in place of a steel plate.

Unlike metals, ceramics are never used alone in armor systems; they are always combined with a ductile backing or support layer of metal or fiber reinforced plastic composite materials, and this ceramic-faced assembly is called ceramic armor. Ceramic materials, like glass, have high hardness and compressive strengths but low tensile strengths. Bonding a ceramic tile to a metallic or composite backing material, with high strength and good ductility, delays or mitigates tensile failure upon impact, and forces the ceramic to fail in compression.

Ceramic armor systems defeat small arms projectiles and kinetic energy penetrators by two main mechanisms: Shattering and erosion. When a hard steel or tungsten carbide projectile hits the ceramic layer of a ceramic armor system, it is momentarily arrested, in a phenomenon known as dwell. Depending on the thickness and hardness of the ceramic layer, the projectile core is then either shattered, fractured, or blunted. The projectile's remnants continue to penetrate the comminuted ceramic tile at a reduced velocity, which erodes those remnants and reduces their energy, length, and mass. The metal or fiber reinforced plastic composite layer behind the ceramic layer then arrests the projectile's fragments or its eroded remnant, and absorbs residual kinetic energy, typically via plastic deformation. If the backing material is too thin or too weak to absorb the residual kinetic energy – or if the projectile does not shatter and the eroded projectile remnant retains too much of its mass and kinetic energy – penetration will occur. Both the ceramic layer and its backing layer are therefore of equal importance.

In vehicular ceramic armor, the backing material is most commonly structural steel, frequently rolled homogeneous armor, though aluminum is sometimes used. In body armor, where ceramic armor designers strive to make ceramic armor plates as light and as comfortable as possible, the backing material is typically a lightweight ultra high molecular weight polyethylene fiber composite, but may also be an aramid fiber composite – and, in low-end ceramic armor plates or in plates for stationary wearers such as helicopter crews, fiberglass is sometimes used.

Against high-explosive anti-tank rounds, the ceramic elements break up the geometry of the metal jet generated by the shaped charge, greatly diminishing penetration.

Ceramic plates are commonly used as inserts in soft ballistic vests. Most ceramic plates used in body armor provide National Institute of Justice Type III protection, allowing them to stop rifle bullets. Ceramic plates are a form of composite armor. Insert plates may also be made of steel or ultra high molecular weight polyethylene.