The Pokédex keeps track of the Pokémon you’ve seen and caught. Use the Pokédex to learn more about the different species of Pokémon and their Evolutions.
Pokémon you’ve caught appear in color. Pokémon you’ve seen but haven’t caught appear as silhouettes; this includes Pokémon seen during encounters as well as at Gyms. Pokémon you’ve neither seen nor caught appear as their Pokédex number.
To access the Pokédex:
  1. In Map View, tap the Main Menu 
  2. Tap Pokédex 

Pokédex Categories

To view unique categories of Pokémon you’ve seen or caught, tap the ALL button on the bottom right-hand corner of the Pokédex screen. You will then be able to select any category that you have unlocked. You must catch a certain number of Pokémon to unlock new categories, so they may not all be immediately available to you. When a new category becomes available, you will be alerted in-game.
Please note that not all categories will backfill Pokémon not in your inventory that you have seen or caught before the rollout has been completed for this feature.
The Shiny and Lucky categories should be backfilled for Pokémon you have seen or caught. The Shadow and Purified categories will be backfilled at a future time.

Searching the Pokédex

As your Pokémon collection grows, you can use keyword searches to quickly and easily search the Pokédex to see details about specific Pokémon.

To search the Pokédex, simply tap the magnifying glass icon in the top right corner of the Pokédex.

Similar to searching your Pokémon Inventory, the Pokédex Search has a set of preset filters that you can use to quickly narrow your search results. Tap on the filter to add it to your search or tap the X button on the filter to remove it.
You can also manually enter a keyword to search for a specific Pokémon. Keyword searches can be used on their own, or in combination with the preset filters. Note that you can use any of the search queries to filter your Pokémon Inventory to also search your Pokédex. See more details here.
You can also use both the preset filters and keyword searches if you are viewing a specific Pokédex (e.g. the Mega Pokédex or the Shadow Pokédex).

To clear your search, simply tap the X icon to the right of the search bar.