Iron ingots can be primarily obtained by Smelting (with the help of a Furnace/Blast Furnace of iron ore found while mining. However, they can also be found in Temples, dungeon, and stronghold Chests. Rarely, Zombies will drop items made of iron, due to them wearing iron armor or holding an iron tool, or just the ingot itself. Iron Golems drop 3 to 5 iron ingots when they die.
Iron is one of the most useful Items in-game, as it creates tools that are capable of mining all ores and anything but Obsidian (which can only be mined with a DiamondPickaxe) and Bedrock. It also creates the second strongest armor, with diamond being the strongest. This makes it perhaps one of the most-used materials in Minecraft.
Iron is used in the most amount of crafting recipes which are about 29 total.
Because it's a rare drop by zombies, iron ingots are considered a renewable resource.
Weaponsmith, armorer, and toolsmith Villagers will buy iron ingots in exchange for Emeralds.