There are 151 Pokémon in "Pokémon GO." The game contains the entire first run of Pokémon, which originally debuted in the mid-'90s.
You cannot, however, catch them all. At least not yet.
The Pokemon Company
TI Executive Editor Alyson Shontell has 143 Pokémon spots in her Pokédex. Video Producer Chris Snyder has 148. He's a level 22!
That original list of 151 includes three "Legendary" Pokémon - Articuno, Zapdos, and Moltres - who definitely aren't in the game yet. It also includes Ditto, Mew, and Mewtwo, who definitely aren't in the game yet. There's also some speculation as to whether certain Pokémon on that list are exclusive to certain territories (Tauros to North America, Mr. Mime to Western Europe, etc). That last bit isn't entirely clear, but seems to be accurate.
Here's what we know: The in-game encyclopedia of Pokémon, the "Pokédex," increases in size as you discover Pokémon (as seen above).
The in-game list is identical to this official list of Pokémon in the online Pokédex, not just in number but in order. One of our staff video producers has a Dragonair (#148). None of us has ever seen a Mr. Mime (#122), but our executive editor has a Tauros (one of the region-specific ones, supposedly tied to North America). No one has found Ditto (#132) anywhere in the world. All of which is to say: Expect the entire line-up of 151 original Pokémon to be capturable at some point. Currently, it looks like each region tops out at 142 - someone in North America claims to have already gotten there!
Without further ado, here's every Pokémon you can currently find in "Pokémon GO."