Attrition warfare is a strategic concept that to win a war, one's enemy must be worn down to the point of collapse by continuous losses in personnel and materiel. The war will eventually be won by the side with greater such reserves.

A well known example of this is during World War I on the western front where both forces found themselves in static defensive positions in trenches that ran from the Swiss Alps to the English Channel. For years without any opportunity for maneuvers, the only way the commanders thought they could defeat the enemy was to continually attack each other head on and to grind the other down. The Battle of the Somme (1916) in World War I is another example, but tanks were introduced in order to try to break the stalemate created by Attrition warfare

The Vietnam War has frequently been called a war of attrition, the American strategy being to wear down the enemy until he lost his "will to fight". Ultimately, this strategy would prove unsuccessful, perhaps due to the asymmetrical nature of the conflict and the profound underestimation by the United States of the determination of North Vietnam.

Most military theorists through history have viewed attrition warfare as something to be avoided. In the sense that attrition warfare represents an attempt to grind down an opponent through superior numbers, it represents the opposite of the usual principles of war, where one attempts to achieve decisive victories through maneuver, concentration of force, surprise, and so forth. On the other hand, a side which perceives itself to be at a marked disadvantage in maneuver warfare or unit tactics may deliberately seek out attrition warfare to neutralize its opponent's advantages. One example would be the late United States Civil War, where Grant pushed the Confederate Army continually in spite of losses, confident that the Union's supplies and manpower could overwhelm the Confederacy even if the casualty ratio was unfavorable.

If the sides are evenly matched or nearly so, the outcome of a War of Attrition may be a Pyrrhic victory.

See also:

• Battle of attrition
• Fabian Strategy
• Maneuver warfare