A ballistic vest or bullet-proof vest is an item of armor that absorbs the impact from gun-fired projectiles and explosive fragments fired at the torso. Soft vests made from layers of tightly-woven fibres protect wearers from projectiles fired from handguns, shotguns, and shrapnel from explosives such as hand grenades. When metal or ceramic plates are used with a soft vest, it can also protect wearers from shots fired from rifles. Soft vests are commonly worn by police forces, private citizens and private security guards, and hard-plate reinforced vests are mainly worn by combat soldiers in the armies of various nations as well as armed response police forces.

Modern body armor may combine a ballistic vest with other items of protective clothing, such as a helmet. Vests intended for police and military use may also include ballistic shoulder armor for more protection and leg armor for protection against grenade blasts.

Vests may be augmented with metal, ceramic or polyethilene plates that provide extra protection to vital areas. These hard armor plates have proven effective against all handgun bullets and a range of rifles. These "tactical body armor" vests have become standard in military use, as soft body armor vests are ineffective against most military rifle rounds. The CRISATNATO(Collaborative Research Into Small Arms Technology-North Atlantic Treaty Organization) standard for body armor specifies the use of titanium backing. This titanium plate may be removable or sewn in.

A vest does not protect the wearer by deflecting bullets. Instead, the layers of material catch the bullet and spread its force over a larger portion of the body, absorbing energy more quickly and hopefully bringing it to a stop before it can penetrate into the body. This tends to deform the bullet, further reducing its ability to penetrate. While a vest can prevent bullet wounds, the wearer still absorbs the bullet's energy, which can cause blunt force trauma. The majority of users experience only bruising, but impacts can still cause severe internal injuries.

Most vests offer little protection against arrows, ice picks, stabbing knife blows, bullets with their points sharpened or armor-piercing rounds. As the force is concentrated in a relatively small area with bladed weapons and armor-piercing rounds, they can push through the weave of most bullet-resistant fabrics. Specially-designed vests which protect against bladed weapons and sharp objects are often used in vests for prison guards and other law enforcement officers. Some materials like Dyneema offer considerable protection against bladed weapons and slash attacks.

Most ballistic vests may provide little or no protection against rifle ammunition or even against handgun ammunition fired from a pistol-caliber carbine. However, vests of type III and up are built to be resistant to rifle and armor piercing rifle fire, the exception being .22 LR ammunition, which can usually be stopped by these vests even when fired from a rifle. These vests are usually protective against handgun ammunition fired from handguns of all calibers, depending on the armor level of the vest

Armor Level	Protects Against
Type I (.22 LR; .380 ACP)	This armor protects against 22 calibre Long Rifle Lead Round Nose (LR LRN) bullets, with nominal masses of 2.6 g (40 gr) at a reference velocity of 329 m/s (1080 ft/s ± 30 ft/s) and .380 ACP Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 6.2 g (95 gr) at a reference velocity of 322 m/s (1055 ft/s ± 30 ft/s)
Type IIA (9 mm; .40 S&W)	This armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) at a reference velocity of 341 m/s (1120 ft/s ± 30 ft/s) and .40 S&W calibre Full Metal Jacketed (FMJ) bullets, with nominal masses of 11.7 g (180 gr) at a reference velocity of 322 m/s (1055 ft/s ± 30 ft/s). It also provides protection against the threats mentioned in [Type I].
Type II (9 mm; .357 Magnum)	This armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) at a reference velocity of 367 m/s (1205 ft/s ± 30 ft/s) and 357 Magnum Jacketed Soft Point (JSP) bullets, with nominal masses of 10.2 g (158 gr) at a reference velocity of 436 m/s (1430 ft/s ± 30 ft/s). It also provides protection against the threats mentioned in [Types I and IIA].
Type IIIA (High Velocity 9 mm; .44 Magnum)	This armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) at a reference velocity of 436 m/s (1430 ft/s ± 30 ft/s) and .44 Magnum Semi Jacketed Hollow Point (SJHP) bullets, with nominal masses of 15.6 g (240 gr) at a reference velocity of 436 m/s (1430 ft/s ± 30 ft/s). It also provides protection against most handgun threats, as well as the threats mentioned in [Types I, IIA, and II].
Type III (Rifles)	This armor protects against 7.62 mm Full Metal Jacketed (FMJ) bullets (U.S. Military designation M80), with nominal masses of 9.6 g (148 gr) at a reference velocity of 847 m/s (2780 ft/s ± 30 ft/s) or less. It also provides protection against the threats mentioned in [Types I, IIA, II, and IIIA].
Type IV (Armour Piercing Rifle)	This armor protects against .30 calibre armour piercing (AP) bullets (U.S. Military designation M2 AP), with nominal masses of 10.8 g (166 gr) at a reference velocity of 878 m/s (2880 ft/s ± 30 ft/s). It also provides at least single hit protection against the threats mentioned in [Types I, IIA, II, IIIA, and III].

BDUs (Battle Dress Uniform) Sizing Chart