Slime Monsters are a set of monsters, identified as slightly transparent blobs that slowly hop toward the player in an attempt to attack. They are most likely going to be the first enemies you find in the game. They are the most common enemies in Terraria, able to spawn at any time of day and in nearly every biome. There are many types, all differing in appearance, stats, and behavior: As a general rule, however, the stronger the slime, the higher and more frequently they will jump at the player. They will all drop gel and coins. A few drop extras, such as the Dungeon Slime drops a Golden Key and the King Slime, being a boss, can drop a multitude of items and the Corrupt Slime and Mother Slime splitting into Slimelings and Baby Slimes.
When a slime is about to hop, it bobs up and down rapidly. Surface slimes such as Green, Blue, or Purple slimes are neutral until they are underground or if it is nighttime or if they were attacked. Otherwise, the rest of the slimes will just remain hostile no matter the location.
Slimes will become passive to the player if they have the Royal Gel equipped.
- Baby Slime
- Black Slime
- Blue Slime
- Dungeon Slime
- Green Slime
- Ice Slime
- Jungle Slime
- Lava Slime
- Mother Slime
- Purple Slime
- Red Slime
- Sand Slime
- Spiked Ice Slime
- Spiked Jungle Slime
- Yellow Slime
- Umbrella Slime
- Corrupt Slime
- Illuminant Slime
- Shadow Slime (console)
- Gastropod 
- Toxic Sludge
- Rainbow Slime
- All Slimes can ascend Wood Platforms, but not descend them due to the fact that they can only jump.
- All Slimes float on water (it is possible to temporarily escape Slimes by going underwater).
- All Slimes are immune to both: Poisoned and Venom debuffs. Illuminant and Lava Slimes are also immune to On Fire!, Cursed Inferno and Shadowflame.
- Blue Slimes and the King Slime can also be spawned by powering a Slime Statue or using a Slime Crown.
- Due to this and the King Slime fight, there are more ways to spawn a Blue Slime than any other slime.
- Yellow Slimes and Purple Slimes seem to spawn more often at dawn after unlocking Hardmode.
- Baby Slimes and Slimelings only spawn off their dead mother counterparts, Mother Slimes and Corrupt Slimes, and Shadow Slime, respectively.
- Small slimes such as Green Slime, Red Slime etc. Sometimes can clip through blocks.
- The Halloween Update (1.2.1) added slimes that have bunny masks, are highly transparent with a slight blue color and have identical stats to a blue slime.
- As of 1.3, slimes can sometimes spawn with items inside them. This has been observed with ores, potions, and coins, and the items are visible inside them. They will always drop a number of them along with their normal drops.
- Slimes have a particular jump pattern. It first jumps 2 small jumps (about 6 blocks) then jumps a higher jump. (about 10 blocks)
- Because it can only jump to move, it may get stuck in a small space.
- Yellow Slimes and Purple Slimes seem to spawn nearer to the edge of the world.
- A player can tell when a slime is about to jump by watching the speed of its animation. When its animation is at full speed the slime will then jump.
- Green Slimes usually are only found in the forest biomes.
- The Royal Gel, an item obtained from slaying King Slime, makes all slimes docile towards the player with the exception of Hoppin' Jacks, Spiked Slimes, and King Slime himself. Please note Gastropods are considered slimes by this rule and are also rendered docile even though killing them does not count for the achievement "Gelatin World Tour".
- Slimes become hostile in behavior at night and in dark areas such as in caverns.
- While their behaviour are different from the common slime enemies, Gastropods are in fact, slime-type enemies accordingly to the game files. This is further reinforced by their shared immunity to Poisoned and Venom, the fact that they drop gel on death and their sound effects when hurt and/or killed.
- Virtually identical slime-like enemies of various colors (as in Terraria) star prominently in the 1984 arcade title "The Tower of Druaga" and it's respective 2008 anime series of the same name.