
Sims live for a set duration of time that is adjustable by the player and advance through several life stages (baby, toddler, child, teen, young adult, adult, and elder). The game includes an optional feature called "Story Progression" which allows all Sims in the neighborhood to autonomously continue free will as if the player were controlling them, such as get married, get jobs and promotions, have children, move into their dream house or move out of the neighbourhood while the player isn't playing, etc. Moodlets can be inspired by physical events, such as having a good meal or comfort from sitting in a good chair, as well as emotional events like a first kiss or a break-up. Fulfilling a Sim's wish contributes to the Sim's Lifetime Happiness score, allowing players to purchase lifetime rewards for the cost of those Lifetime Happiness points. The all new reward system Wishes replaces the Wants And Fears system in its predecessor The Sims 2. If the opportunity is connected to a Sim's school, the reward may be increased school performance. Skill opportunities are requests by neighbors or community members for Sims to solve problems using their acquired skills for cash or relationship rewards. Career opportunities such as working overtime or completing special tasks can yield a pay raise, cash bonus, or relationship boost. Challenges occur randomly based on aspects of each Sim's lifestyle, such as relationships, skills and job.

The gameplay is open-ended and does not have a defined goal.

Players control their own Sims' activities and relationships in a manner similar to real life. The Sims 3 is built upon the same concept as its predecessors.
