Pokémon Labs are the places where Pokémon Professors (Oak, Elm, Birch, Rowan, or Juniper) give the Trainer a Starter Pokémon in the beginning.
Professor Oak is featured in Pokémon Red, Blue and their remakes, FireRed and LeafGreen. In these games, Oak either gives the Trainer a Bulbasaur, a Charmander or a Squirtle, but in Pokémon Yellow he gives the Trainer a Pikachu.
Professor Elm is featured in Pokémon Gold, Silver, Crystal and their remakes, HeartGold and SoulSilver. In these games, Elm either gives a Chikorita, a Cyndaquill or a Totodile to the Trainer. This Pokémon lab is in New Bark Town.
Professor Birch is featured in Pokémon Ruby, Sapphire and Emerald. In these games, Birch either gives the Trainer a Treecko, a Torchic or a Mudkip.
Professor Rowan is featured in Pokémon Diamond, Pearl and Platinum. In these games, Rowan either gives the Trainer a Turtwig, a Chimchar, or a Piplup.
Professor Juniper is featured in Pokémon Black and White. In these games, Juniper either gives the Trainer a Snivy, a Tepig or an Oshawott.
Each Generation has three different starter Pokémon, all of whom are Grass, Fire or Water-type Pokémon.