Collecting (The Sims 4)

The Sims 4 has revamped item collection from The Sims 3, making it a larger aspect of the game and linking various Aspirations to it. There are currently 13 collections in the base game, one additional collection temporarily added with a patch, one additional collection added with The Sims 4: Outdoor Retreat, and one additional collection added with The Sims 4: Get to Work.

Aliens
There are 10 Aliens that can be collected, and they are collected through Space Exploration on a Rocket Ship.

Crystals
There are 20 Crystals that can be collected, and they are collected through exploring various Rocks in the world.

Elements
There are 15 Elements that can be collected, and they are collected through sending Crystals and Metals to the Geo Council.

Fish
There are 22 types of fish that can be collected (27 with Outdoor Retreat), and they are collected through fishing at various places in the world.

Fossils
There are 15 Fossils that can be collected, and they are collected through exploring various Rocks in the world.

Frogs
There are 25 Frogs that can be collected, and they are collected in Logs, Ponds or farmed through Breeding.

Gardening
There are 32 Plants that can be collected, (42 with Outdoor Retreat) and they are collected through finding them in the wild or Grafting them together to earn rare specimens.

Metals
There are 20 Metals that can be collected, and they are collected through exploring various Rocks in the world.

Microscope Prints
There are 12 Microscope Prints that can be collected, and they are collected through Analyzing Plant/Fossil Samples on a Microscope.

MySims Trophies
There are 20 MySims Trophies that can be collected, and they are collected through exploring Rocks in the world, then finding a capsule. Opening it grants a MySims trophy.

Postcards
There are 14 Postcards that can be collected, and they are earned through getting Pen Pals, and talking with them enough to ask for a postcard.

Space Prints
There are 15 Space Prints to be collected, and they are earned through Stargazing/Observing the Sky using the Observatory.

Space Rocks
There are 4 Space Rocks to be collected, and they are collected through Space Exploration on a Rocket Ship.

Decorative Eggs
There are 10 Decorative Eggs to be collected. This collection was introduced in patch 15, and until patch 17 the "Bunny Egg Hunt" challenge could be collected through harvesting plants, collecting mail, opening capsules found by excavating rocks, and looking in logs. Completing this collection unlocked a giant stuffed animal.

Sugar Skulls
There are 10 Sugar Skulls to be collected. This collection was introduced in the patch 41, and until the "Day of the Dead" challenge could be collected through asking Day of the Dead celebrators. Completing this collection will allow Sims to use the "Honor the Dead" interaction granting them the "Day of the Dead Celebrant" moodlet which will boost interactions with the Grim Reaper.

Collections from the Expansion/Game Packs
The Sims 4: Outdoor Retreat

Insects
There are 21 insects to collect, and they are collected through searching for them in the Granite Falls world.

Voidcritter Cards
There are 20 Voidcritter cards to collect. Children can find them through a new Interaction, exclusive to Kids Room Stuff. This interaction allows children to search through trash for the collectibles. Alternatively, they can be purchased from a Computer or children can trade them with other Sims. These cards come in booster packs.