Interactions are certain limited acts which Sims can do to or with objects, Sims, pets, etc. Interactions with objects are usually related to the object's use, however, downloading certain hacks or mods, or using certain cheats, might increase the number of interactions an object has, or even create interactions which have no relation with the object. Interactions with Sims increase and decrease relationships. Self-interactions, which can be selected when the player clicks on the selected Sim, tell that Sim to perform certain actions.

Interactions with people are dependent on their level of relationship and life stages which have their own special interactions.

There are four different types of interactions: One-Time, Timed, Endless and Autonomous.

• One-Time: The interaction is performed once meaning that there is no time limit to these interactions- they can be performed repeatedly. Most interactions between Sims are of this type. These can include, but are not limited to: chatting, playing games (like rock paper scissors, tag, cops and robbers, etc.), romantic acts, fighting (physical and verbal) and greeting neighbors as they walk by.
• Timed: The interaction is performed until the task is complete, or until it is canceled. These are usually cooking and cleaning chores but playing chess and pool is also an example of this type of interaction.
• Endless: The interaction is performed endlessly until the related motive reaches maximum, or another motive needs to be tended, such as going to the bathroom. The only exceptions to this rule are the fun and comfort motives- interactions related to these are only stopped by the player or when another more critical need must be filled.
• Autonomous: These are interactions that are done during a Sim's free time. Examples are howling (werewolves), stalking and Bleh! (vampires), acting very happy and waving their wands (good witches), laughing maniacally (evil witches), and cheering (cheerleaders and mascots).