Theme

Each expansion pack for a The Sims is centered around one or more themes.

Dating
Dating was added with The Sims: Hot Date and reintroduced with The Sims 2: Nightlife. Dating is included in The Sims 3 base game, though it is simplified from previous games. The Sims 3: Late Night may expand upon it.

Cars
Personal car ownership was introduced in The Sims 2: Nightlife and was incorporated into The Sims 3 base game. The Sims 3: Fast Lane Stuff will add new cars.

Parties
Parties, while always possible to some extent, were the main theme of The Sims: House Party. The Sims 2 added theme parties such as house parties, birthday parties, wedding parties and anniversary parties. The Sims 2: University added sports parties and toga parties and The Sims 2: Apartment Life added apartment parties and building parties. In The Sims 3 base game, you can choose between house parties, birthday parties or funerals, but you have the option of throwing them at a community lot.

Pets
Pets are introduced in The Sims: Unleashed and reintroduced in The Sims 2: Pets. All versions of The Sims have had aquariums, fish that require a minimum of maintenance, although The Sims 3 and The Sims 3: World Adventures allow the keeping of bugs, butterflies, snakes, frogs, snails and crocodiles, as well as other fish.

Gardening
Gardening was added in The Sims: Unleashed and brought back in The Sims 2: Seasons. Planting seeds and other gardening activities are included in The Sims 3.

Vacations
Vacationing was added with The Sims: Vacation, then again with The Sims 2: Bon Voyage, and a similar "travel & adventure" theme is the basis of The Sims 3: World Adventures.

Magic
Magic was the centerpiece of The Sims: Makin' Magic as was reintroduced in The Sims 2: Apartment Life.

Fame
Being famous was the main theme of The Sims: Superstar. Fame was not incorporated into The Sims 2 series at all, though Sims could have reputation in The Sims 2: Apartment Life. Fame is found to a lesser degree in The Sims 3 music career, but is a major feature of The Sims 3: Late Night.

College life
The central theme of The Sims 2: University, adding the Young adult life stage and University campus sub-neighborhoods.

Weather
Main theme of The Sims 2: Seasons. Added four possible seasons for Neighborhoods: Spring, Summer, Fall/Autumn & Winter. While it is possible to achieve some weather effects with the Fog Emitter in The Sims 3, the concepts of weather has not been fully implemented. But in The Sims 3 Console it is said there is gonna be weather for the Wii version of it.

Businesses
The idea of Sims managing their own businesses was central to The Sims 2: Open for Business, and was included in The Sims 3, though business ownership was simplified and businesses could not be founded independently or formed on private lots. The Sims 3: Ambitions expanded on the real estate market a bit and also made it possible to sell crafted items at a Consignment store.

Apartments
Created in The Sims 2: Apartment Life, but left out of The Sims 3. A simplified version of apartments will be introduced in The Sims 3: Late Night this does not however include communal living. It is merely like a regular house where only the top floor is accessible.

Hobbies
Hobbies was a theme in The Sims 2: FreeTime and The Sims 3: Ambitions.

Luxury
High End Living was always possible, and expansion packs would frequently add some high-end objects. It was also a theme, though perhaps not a major theme, of The Sims: Livin' Large. It was also a theme of The Sims 2: Glamour Life Stuff, The Sims 2: Mansion & Garden Stuff, and The Sims 3: High-End Loft Stuff.