Professor Oak's Laboratory (Japanese: オーキド研究所Okido Institute), also called the Oak Pokémon Research Lab (Japanese: オーキド博士のポケモン研究所Professor Oak's Pokémon Research Lab), is a Pokémon lab located in Pallet Town that is directed by Professor Samuel Oak. Its functions are to research Pokémon, unravel the mysteries of these creatures, and study their characteristics and behavior in a natural environment. Another important job is to take care of the Pokémon that belong to Pallet Town's Trainers.
The lab has many different environments for the correct development of all kinds of Pokémon. There are areas of grass, sand, rocks and lakes to promote good interaction between the different types of creatures. The laboratory has the technology to keep Pokémon healthy, and to make the largest scientific investigations in the country.
The lab is a small building near the player's house that has been slightly modified in every game.
In Pokémon Red and Blue, the sign says "Oak Pokémon Research Lab" ("Here is the Institute of Dr. Okido." in Japanese). Inside are three of Professor Oak's aides, two men and one woman, a couple of shelves full of books, a table with three Poké Balls, a computer, two blank Pokédexes, and two tips for the player.
In Pokémon Yellow, the lab is the same as Red and Blue, except there is only one Poké Ball on the table, and next to the table stands a trash can.
In Pokémon Gold, Silver, and Crystal, the lab is almost unchanged except recoloring, only adding two windows, removing a table and adding another shelf to bookshelves.
In Pokémon FireRed and LeafGreen, other than the significant graphical enhancements, the laboratory also has two plants in the entrance, a mysterious machine, books on the floor, two regular machines in the corner, and a window.
In Pokémon Puzzle League for the Nintendo 64, an area called "Prof. Oak's Labs" acts as tutorial area. Professor Oak will teach the player how to play the game.
Professor Oak's Laboratory also appears in Pokémon Snap, shown as the background of the main menu of the game. Todd Snap reports back here regularly to show his photos to Professor Oak. Presumably, the professor keeps information like the Pokémon Report, Pokémon Album, and all information on Pokémon signs in his laboratory. It appears the same way in this game that it does in the anime.
Every time Ash catches a Pokémon when he has already a full party, the new Pokémon is automatically transported here. Ash also has a habit of leaving all of his Pokémon besides Pikachu here each time he leaves for a new region, starting with Hoenn.
The lab is composed of two floors. Inside the entrance door is a hallway with several doors, and to the left is a chest of drawers and the stairway to the second floor.
The living room is the space where Professor Oak hosts, eats, relaxes, and presumably studies. On a pink carpet (sometimes shown as green) are two couches and a table. To the side are a computer and bookshelves. This is where many scenes in the lab take place. There are also two science rooms full of various machines.
The Poké Ball Storage Room stores the extra Pokémon of every Trainer born in Pallet Town. This treasure of hundreds of Pokémon has been the target of attempted robberies by Team Rocket. In addition, the lab has a library, composed of two rooms. One is a study room with a large bookshelf and a pair of windows. The other, in the back, is a storage room full of books, including Oak's old sketchbook.
The study room of Professor Oak
Upstairs is the research floor. Here are all the technological pieces, the heart of the laboratory. It includes several machines used for Pokémon testing and a table with various chemicals on it. Nearby is a blue chair. In front of it are the status screen, which shows the health and power of a Pokémon, and Professor Oak's computer, where he records his research. This computer doubles as a videophone, which he uses to communicate with other professors or Trainers. Beside the computer is the Poké Ball Transfer machine, for the transportation of Pokémon to their Trainers in a Pokémon Center. The room also includes a bookshelf, a desk with a lamp, a brown couch, and a drawing board. A few machines are connected to a glass container full of water, possibly to study aquatic Pokémon. Hanging from the ceiling is a large lamp.
The stairs lead up to an inner balcony, which has a door and the three large windows seen in most outside views of the lab.
A full view of the research floor
The Oak Corral is a natural environment for Pokémon development. It is divided into regions according to type; there are areas that are perfect for Rock Pokémon, desert areas for Ground and Fire types, grassy regions, and several lakes. Sometimes the Pokémon don't get along; for this reason, some Pokémon, such as Ash's Bulbasaur, act as mediators between quarreling Pokémon.
Professor Oak's Laboratory first appeared in File 1: Red, where Red and Blue got their first Pokémon and Pokédexes from Professor Oak. In File 4: Charizard, Red returned to the lab after having caught all 149 known Pokémon. Later, after Red had successfully caught Mewtwo in Cerulean Cave, Professor Oak held a minor celebration at the laboratory to congratulate Red and Blue on completing of the Pokédex, although Red soon realized that Mew still remained uncaught.
The laboratory first appeared in A Glimpse of the Glow, where Red went to see Professor Oak. The first view of the inside of the lab was seen in Bulbasaur, Come Home!, and was shown to have machines, tables, bookshelves, a glass container full of water and a Poké Ball storage area. Red accidentally let all the Pokémon in the laboratory out of their Poké Balls, with some even escaping the building altogether, forcing Red and Professor Oak to chase them.
In Kalling Kadabra, Sabrina's Kadabra disguised itself as Professor Oak, rampaging around the place in front of Red. Sabrina herself also briefly appeared, giving Red a message to come to Saffron City. Blue then arrived with his Charizard, showing Red a picture of Saffron City, which had been taken over by Team Rocket and was where they kept the citizens of Pallet Town they had imprisoned.
The laboratory was once again seen in Return to Pallet Town, when Red and Blue received messages from Professor Oak to return their Pokédexes. This was later revealed to be a trap set by Team Rocket, intending to force Professor Oak to create them their own version of the Pokédex in preparation to capture Deoxys.
In Generation I games, there is a moment when it is possible to stop the game. This happens if the player holds the A button after choosing their starter, which will stop Blue from choosing his own starter until the player releases the button. This happens in all Generation I games, but is easier to perform in Yellow. 
If the player's Pokémon takes damage in his/her first battle against their rival in FireRed and LeafGreen, their Pokémon will be healed after the battle.
Professor Oak's lab's iconic theme is not played in Generation IV, with the background music instead being Pallet Town's theme. The only way to hear the lab theme is to listen to the Pokégear radio.
In Pokémon Yellow, there is a trash can in between the table and the right wall containing the starter Pokémon, unlike in Pokémon Red and Blue. This effectively blocks the player from walking to the other side of the table to collect Eevee where the rival can't push them.