Back in Pokemon Yellow so long ago, Pikachu would Follow closely behind your trainer wherever they would go (sort of like Ash Ketchum's Pikachu in the Pokemon Anime Series). This same concept was seen in Pokemon HeartGold and Pokemon SoulSilver, and now it's returning once again in Pokemon: Let's Go, Eevee!
On top of having your trusty Eevee staying put on top of your trainer's cap at all times, players will also be able to assign another Pokemon to Follow them around outside of their Poke Ball. Sometimes, these Pokemon will even find an item hidden in the wild! Furthermore, should you set a larger Pokemon to follow you, there is a chance that your trainer might even be able to Ride them!