List of Field Research tasks and rewards

Please, note that there are always only either: specific amount of stardust, or XP, or just one kind of item, or a particular Pokémon encounter for a single task completed, which means only one of following possible rewards is rewarded for single Field Research task completed not all of them!

April 2018 tasks
Theme for Field Research tasks in April 2018 was Fire-type Pokémon.

Catching Pokémon related tasks
Following tasks were related to Catching Pokémon through the Encounter Screen. To complete any of following tasks, Trainer had to successfully capture Pokémon, which was either approached in the wild, from Raid Bonus Challenge or reward encounter for other, already completed Research task.

Throwing Poké Balls related tasks
Following tasks were related with performance of throwing any of Poké Balls when catching Pokémon.

Gym and Raid Battle related tasks
Following tasks were related with battling a Gyms or Raid Battles.

Other tasks
Following tasks were related with Hatching Pokémon Eggs, evolving or power-upping Pokémon, earning Candy with Buddy and other basic game actions.

May 2018 tasks
Theme for Field Research tasks in May 2018 was Electric- and Flying-type Pokémon.

Catching Pokémon related tasks
Following tasks were related to Catching Pokémon through the Encounter Screen. To complete any of following tasks, Trainer had to successfully capture Pokémon, which was either approached in the wild, from Raid Bonus Challenge or reward encounter for other, already completed Research task.

Throwing Poké Balls related tasks
Following tasks were related with performance of throwing any of Poké Balls when catching Pokémon.

Gym and Raid Battle related tasks
Following tasks were related with battling a Gyms or Raid Battles.

Other tasks
Following tasks were related with Hatching Pokémon Eggs, evolving or power-upping Pokémon, earning Candy with Buddy and other basic game actions.

June 2018 tasks
Theme for Field Research tasks in June 2018 was Water-type Pokémon.

Catching Pokémon related tasks
Following tasks were related to Catching Pokémon through the Encounter Screen. To complete any of following tasks, Trainer had to successfully capture Pokémon, which was either approached in the wild, from Raid Bonus Challenge or reward encounter for other, already completed Research task.

Throwing Poké Balls related tasks
Following tasks were related with performance of throwing any of Poké Balls when catching Pokémon.

Gym and Raid Battle related tasks
Following tasks were related with battling a Gyms or Raid Battles.

Other tasks
Following tasks were related with Hatching Pokémon Eggs, evolving or power-upping Pokémon, earning Candy with Buddy and other basic game actions.

July 2018 tasks
Theme for Field Research tasks in July 2018 was Kanto-region Pokémon.

Catching Pokémon related tasks
Following tasks were related to Catching Pokémon through the Encounter Screen. To complete any of following tasks, Trainer had to successfully capture Pokémon, which was either approached in the wild, from Raid Bonus Challenge or reward encounter for other, already completed Research task.

Throwing Poké Balls related tasks
Following tasks were related with performance of throwing any of Poké Balls when catching Pokémon.

Gym and Raid Battle related tasks
Following tasks were related with battling a Gyms or Raid Battles.

Other tasks
Following tasks were related with Hatching Pokémon Eggs, evolving or power-upping Pokémon, earning Candy with Buddy and other basic game actions.

August 2018 tasks
Theme for Field Research tasks in August 2018 was Electric-type Pokémon.

Catching Pokémon related tasks
Following tasks were related to Catching Pokémon through the Encounter Screen. To complete any of following tasks, Trainer had to successfully capture Pokémon, which was either approached in the wild, from Raid Bonus Challenge or reward encounter for other, already completed Research task.

Throwing Poké Balls related tasks
Following tasks were related with performance of throwing any of Poké Balls when catching Pokémon.

Gym and Raid Battle related tasks
Following tasks were related with battling a Gyms or Raid Battles.

Other tasks
Following tasks were related with Hatching Pokémon Eggs, evolving or power-upping Pokémon, earning Candy with Buddy and other basic game actions.

September 2018 tasks
Theme for Field Research tasks in September 2018 was Fire-type Pokémon.

Catching Pokémon related tasks
Following tasks were related to Catching Pokémon through the Encounter Screen. To complete any of following tasks, Trainer had to successfully capture Pokémon, which was either approached in the wild, from Raid Bonus Challenge or reward encounter for other, already completed Research task.

Throwing Poké Balls related tasks
Following tasks were related with performance of throwing any of Poké Balls when catching Pokémon.

Gym and Raid Battle related tasks
Following tasks were related with battling a Gyms or Raid Battles.

Other tasks
Following tasks were related with Hatching Pokémon Eggs, evolving or power-upping Pokémon, earning Candy with Buddy and other basic game actions.

October 2018 tasks
Theme for Field Research tasks in October 2018 is Water-type Pokémon.

Catching Pokémon related tasks
Following tasks are related to Catching Pokémon through the Encounter Screen. To complete any of following tasks, Trainer has to successfully capture Pokémon, which is either approached in the wild, from Raid Bonus Challenge or reward encounter for other, already completed Research task.

Throwing Poké Balls related tasks
Following tasks are related with performance of throwing any of Poké Balls when catching Pokémon.

Gym and Raid Battle related tasks
Following tasks are related with battling a Gyms or Raid Battles.

Other tasks
Following tasks are related with Hatching Pokémon Eggs, evolving or power-upping Pokémon, earning Candy with Buddy and other basic game actions.

Event-only tasks
Following Field Research tasks were available during the certain events.

Community Day tasks
Following is the list of research tasks exclusively available only for the time of specific Community Days.

Adventure Week 2018 tasks
Following is the list of research tasks exclusively available only for the time of Adventure Week in 2018. There was a possibility to encounter shiny variants of Omanyte, Kabuto and Aerodactyl as the reward for these tasks.

Water Festival 2018 tasks
Following is the list of research tasks exclusively available only for the time of Water Festival in 2018. There was a possibility to encounter shiny variants of Shellder, Magikarp and Wailmer as the reward for these tasks. The last two tasks were added in the latter half of the event.

GO Fest 2018 tasks
Following is the list of research tasks exclusively available only for the time of GO Fest in 2018. It was available only for attendants of the Fest in Chicago, Illinois, on July and, 2018. As seen all 4 of the tasks rewarded trainers with a single Rare Candy.

Johto Festival 2018 tasks
Following is the list of research tasks exclusively available only for the time of Johto Festival in 2018. These tasks gives Trainers opportunity to complete their Johto Pokédexes and complete A Ripple in Time, the Special Research tasks series. There was a possibility to encounter shiny variants of Pineco as the reward for these tasks. Additionally, these tasks for the first time in game's history rewarded Trainers for completing them with Evolution Items.

Pokémon World Championships 2018
During the time of Pokémon World Championships in Nashville, that took place in the later part of August, 2018, there was a single Field Research task available from PokéStops in 1 mile from the Championships.

Trivia

 * If a Trainer encounters a shiny Pokémon as a research reward, said Pokémon will remain shiny until the Trainer captures it. The Trainer is free to run away and re-encounter the Pokémon and it will always be shiny.