Infantry are soldiers that directly confront the enemy, to defeat them with maneuver, individual weapons fire, the fire of light support weapons directly assigned to their unit, and by directing fires from artillery and close air support. Combat teams that include infantry, armored vehicles, artillery, aviation reporting to the ground commander, and combat engineers conduct combined arms operations.
To Close with and Destroy the enemy day or night; regardless of weather or terrain. — Role of the Canadian Army Infantry
Infantry comprised the very first forms of military, before cavalry and artillery were invented. The Macedonian phalanx, the Roman legions, the archers and pikemen at the Battle of Agincourt — all were ancestors of today's soldiers joined by electronics that turn night into day -- and have robots to carry their heavy equipment. Even in the ancient period, infantry was differentiated in various ways: light infantry wore minimal armor and were the most mobile, while heavy infantry were armored and fought from tight formations.
Infantry are differentiated by the way they move into battle, and sometimes the way they fight (i.e., other than on foot):
- regular: move and fight on foot, possibly brought near the battlefield by trucks that do not go into combat. The latter is sometimes called motorized infantry, or, not just in older times but with special operations forces working with guerrillas, mounted infantry that go to the battle area on horseback, but dismount before combat.
- mechanized infantry: move by vehicles with light to medium armor, in some cases fighting from the vehicle, or dismounting to fight while heavier weapons on their armored personnel carrier (APC) or infantry fighting vehicle (IFV) support them.
- paratroopers: parachute into the battle area or very near it
- air assault: while parachuting is actually a subset, air assault or airmobile infantry are principally carried to battle with helicopters. As with mechanized infantry, dismounted soldiers may received fire support from the lightly armed helicopters that carried them to the battlefield, or from heavier attack helicopters that travel with them
- naval infantry: in amphibious warfare, troops move from the sea either to a direct combat area, or to a less defended area from which they move to attack objectives. The specialists here are often called Marines, or, in Soviet/Russian doctrine, naval infantry. Simply moving by sea to a safe port does not constitute an amphibious operation.
These various types may have special training and equipment for specific environments, such as mountain warfare, arctic combat, jungle warfare, etc. There is a spectrum from regular infantry; to highly trained but still basically conventional soldiers such as Rangers and medium-range reconnaissance units;to units qualified for special reconnaissance and guerrilla warfare deep behind enemy lines.
The basic weapon of an infantryman is a rifle, although soldiers whose primary duty is to be part of a weapons crew, or operating sensors and communications, may have a lighter weapon (e.g., carbine or pistol) that is less likely to get in the way of their primary task. Still, there is a mystique to the rifle:
This is my rifle. There are many like it, but this one is mine. It is my life. I must master it as I must master my life. Without me my rifle is useless. Without my rifle, I am useless. I must fire my rifle true. I must shoot straighter than the enemy who is trying to kill me. I must shoot him before he shoots me. I will. My rifle and I know that what counts in war is not the rounds we fire, the noise of our burst, or the smoke we make. We know that it is the hits that count. We will hit.
My rifle is human, even as I am human, because it is my life. Thus, I will learn it as a brother. I will learn its weaknesses, its strengths, its parts, its accessories, its sights and its barrel. I will keep my rifle clean and ready, even as I am clean and ready. We will become part of each other. Before God I swear this creed. My rifle and I are the defenders of my country. We are the masters of our enemy. We are the saviors of my life. So be it, until victory is America's and there is no enemy.
— United States Marine Corps rifleman's creed
In addition to the basic weapon, the infantryman may have edged weapons of combat knife or bayonet, yet still in the tradition of the sword. Other individual weapons include thrown and launched grenades, portable guided missiles, and explosives, as well as helping carry ammunition for crew-served weapons. Increasingly, modern infantrymen carry a range of military electronics, including radios, night vision devices or thermal viewers, navigational equipment such as a Global Positioning System (GPS) receiver, and laser designators to direct heavy fires onto target.
While mechanized and air assault infantry do have accessible storage on hand, the infantryman carries necessities: water, food, ammunition, batteries, and minimal shelter.
While the specific methods differ with nation, and infantry organization, the smallest unit of regular infantry (as distinct from behind-the-lines special operations unitss, a fire team of 3 to 5 soldiers. Fire teams mutually support one another, one providing fire to distract the enemy from movement of another. Fire teams form squads of 10-13 men; a squad will usually have at least one heavier weapon, such as a machine gun. Squads form platoons of 20-50 men, with a small leader group, additional heavy weapons, and often medical support. Several platoons form a company (land forces) of 100-200 soldiers, with additional leadership, communications and sensors, heavy weapons, and supply.
In modern militaries, units above the company level tend to be teamed with other combat arms to form balanced combined arms teams. Nevertheless, the term "infantry" will extend to organizations as large as divisions of 25,000 or so soldiers.
Infantry operations build up from the smallest units of squads or platoons, with 3-5 man fire teams operating within them. The eight basic U.S. Army infantry battle drills are: 
- Platoon Attack
- Squad Attack
- React to Contact
- Break Contact
- React to Ambush
- Knock Out Bunkers
- Enter Building/Clear Room
- Enter/Clear Trench
- Conduct Initial Breach of a Mined Wire Obstacles
Among other skills, and working under standard command and control doctrine,  they must be able to deliver fire, operate in combined operations with armored vehicles, etc.
- ↑ United States Army Infantry School (January 1996), Lesson 4: BATTLE DRILLS, Infantry Squad Operations, Subcourse Number IN 0201, Edition B
- ↑ United States Army Infantry School (January 1996), Lesson 2, Operations, Operations, Subcourse Number IN 0201, Edition B
- ↑ United States Army Infantry School (January 1996), Chapter 2, Part M, Techniques of fire, Infantry Squad Operations, Subcourse Number IN 0201, Edition B
- ↑ United States Army Infantry School (January 1996), Chapter 2, Part I, Armored Vehicle Support, Infantry Squad Operations, Subcourse Number IN 0201, Edition B