Modern warfare is warfare that diverges notably from previous military concepts, methods, and technology, emphasizing how combatants must modernize to preserve their battle worthiness. As such, it is an evolving subject, seen differently in different times and places. In its narrowest sense, it is merely a synonym for contemporary warfare.

In its widest sense, it includes all warfare since the "gunpowder revolution" that marks the start of early modern warfare, but other landmark military developments have been used instead, including the emphasis of artillery marked by the Crimean War, the military reliance on railways beginning with the American Civil War, the launch of the first dreadnought in 1905, or the use of the machine gun, aircraft, tank, or radio in World War I.

In another sense, it is tied to changing conventional warfare, including total war, and industrial, mechanized, and electronic warfare. It can describe warfare resulting from the use or threats of weapons of mass destruction, including chemical, biological, radiological, and nuclear warfare. It can describe asymmetric warfare, involving violent non-state actors, guerilla warfare, low-intensity conflict, and counter-insurgency. It can also describe the expansion of warfare to new domains, including space warfare and cyberwarfare, as well as psychological warfare and information warfare.

Some argue that the changing forms of third generation warfare represents nothing more than an evolution of earlier technology.

Aerial warfare is the use of military aircraft and other flying machines in warfare. Aerial warfare includes bombers attacking enemy concentrations or strategic targets; fighter aircraft battling for control of airspace; attack aircraft engaging in close air support against ground targets; naval aviation flying against sea and nearby land targets; gliders, helicopters and other aircraft to carry airborne forces such as paratroopers; aerial refueling tankers to extend operation time or range; and military transport aircraft to move cargo and personnel.

A military situation in which two belligerents of unequal strength interact and take advantage of their respective strengths and weaknesses. This interaction often involves strategies and tactics outside conventional warfare.

Biological warfare, also known as germ warfare, is the use of any organism (bacteria, virus or other disease-causing organism) or toxin found in nature, as a weapon of war. It is meant to incapacitate or kill enemy combatants. It may also be defined as the employment of biological agents to produce casualties in man or animals and damage to plants or material; or defense against such employment. Biological warfare involves the intentional release of living pathogens either in their naturally occurring form, for example the diseased corpses of animals, or in the form of specific human-modified organisms.

Chemical warfare is warfare (associated military operations) using the toxic properties of chemical substances to incapacitate or kill enemy combatants. Chemical warfare nerve agents are potent anticholinesterase compounds deliberately formulated to induce debilitating effects or death during wartime hostilities. A key need for both community emergency preparedness, and restoration of military installations where agents have been processed and/or stored, is access to concise and timely information on agent characteristics and treatment, as well as health-based exposure guidelines derived in a clear manner by contemporary methods of data analysis.