Pet Journal
The Pet Journal is a window tab found in the Collections interface. It provides listings and details concerning non-combat pets both collected and not collected, as well as allowing players to queue for pet battles as part of the Pet Battle System. It also provides access to the 
[Revive Battle Pets] ability, as well as the 
[Summon Random Favorite Battle Pet] ability used to select a particular pet to be the player's in-game companion.
Notes
The left-most pane provides a list of all pets (both collected and not collected), with a search function and a choice of filters.
The top-right pane displays the stats and abilities and other information on any pet which is dragged to that pane.
The bottom-right pane consists of three Battle Pet Slots. Dragging a pet to one of these slots will make it part of your current battle pet team, replacing any pet previously occupying that slot. Each Battle Pet Slot displays a review of the pet, showing the pet's name, type, abilities, level, health and experience. Pets' abilities can also be chosen in this pane. Pets will be displayed in-combat in the order of the slots that they occupy; when battling wild pets, the pet in the first slot will always open combat.
At the bottom-left of the window is the [Summon Random Favorite Battle Pet] ability, allowing a pet to be summoned as the player's in-game companion. At the top-right can be found the [Revive Battle Pets] ability, while at the bottom-right is the 'Find Battle' button, queueing the player for a PvP pet battle match against another player with a reasonably similar team of pets.
The window also displays the total number of pets owned by the player, and the player's total Battle Pet Achievements score.
For a listing of all known pets see the list of companions.
Summoning commands
To summon a random pet from the journal, use
/randompet
To summon a random favourite pet, use
/rfp
To summon a specific pet by name (works with either a given name or the default name), use
/summonpet name
Gallery
The Pet Journal since Mists of Pandaria
Pet Journal gifts
The Pet Journal concepts
The Cataclysm design
The first design
Patch changes
Patch 10.0.0 (2022-10-25): UI refresh. 
Patch 7.3.0 (2017-08-29): A “Summon Random Favorite Battle Pet” button has been added to the Pet Journal. 
Patch 5.1.0 (2012-11-27):
- The quality of each pet is now visible in its slot in the Pet Journal.
- Pets can now be filtered by name, type, rarity and level, and filters will remain in place each time the Pet Journal is viewed.
- It is now possible to search locations in the Pet Journal. For example, searching “Westfall” will display all the Battle Pets that can be found in Westfall.
- Patch 5.0.4 (2012-08-28): Redesigned and moved from the Spellbook & Abilities interface to the newly created Mounts And Pets interface. Renamed to Pet Journal from the companions tab.
Patch 4.0.1 (2010-10-12): Redesigned and moved from the character info interface to the Spellbook & Abilities interface. 
Patch 3.0.2 (2008-10-14): Added to the character info interface, under the pets tab.
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