The siege was the most common form of combat in the period. In most cases a siege consisted of little more than a larger army cornering a smaller force holed up inside fortifications. The besieger could try and attack the fortifications, but this would often be risky (for the attacker) and expensive (in terms of dead attackers). The most common tactic was to try and starve the besieged force out. This took time, and given the expense of maintaining a large besieging force over many months, the siege was often lifted because the besieging commander ran out of money to pay his troops.

When an assault on the fortifications was contemplated, it was often assisted by the use of "siege engines." The most formidable of these was the trebuchet. This was, in effect, a large catapult. Some have been built in this century to see just what a trebuchet was capable of. One of these modern trebuchets (a twenty foot long model) could throw a 112 pound weight 230 yards, a 550 pound pig 200 yds, and a 700 pound piano 150 yards. Dead animals were often hurled into the besieged city to spread disease, pigs being favored because they were more aerodynamic. A trebuchet used by the crusaders was dismanteled in 1291 at Acre and required a hundred carts to move. In 1304, king Edward I ordered the construction of a trebuchet that took five foremen and fifty carpenters to build.

In the late 14th century cannon technology had matured to the point where effective cannon for sieges were available. Early cannon were cast by bell makers using much the same technology applied to casting bells. However the soft bronze used wore out quiclkly and reduced the force of the explosion. In 1375 the French built one of the early successful cannon. Four ironsmiths, eight assistants and one laborer built three forges in Caen and worked 2,300 pounds of iron. The gun was made from longitudinal strips of iron welded together and bound with 90 pounds of rope. It was reported that during the siege of Odruik in 1377, 200 pound stone balls were fired. Also in 1377, a canon was ordered to launch 450 pound shot. At Odruik, the Duke of Burgundy fielded 140 canon. It was reported by Froissart that earlier that year at the siege of Ardes, the French canon pierced the walls. This was the first record of a wall being pierced by cannon shot. Eventually the cannon helped bring about the downfall of smaller nobles who could not afford to construct "cannon resistant" fortifications.