You can think of 갔었던 as an emphasized form of 갔던 without clear distinction in meaning. The verb stem 갔 and 갔었 are more distinctive when they are used as a predicate at the end of a sentence. For example, compare these different tense examples based on 이민 가다 (immigrate): 1 친구는 이민 간다 -> 이민 가는 친구- He is going now (or in the near future). 2 친구는 이민 갔다 -> 이민 간 친구. He has gone, and not here anymore. 3 친구는 이민 갔었다 -> 이민 [갔던 / 갔었던] 친구. He had gone, and may have subsequently come back. The difference between 갔다 and 갔었다 is huge, as it is the difference between whether he's here(the latter) or not. Confusingly though, the difference between 갔던 and 갔었던 is almost nonexistent. (The reason for this is because the ending 던 already has a strong sense of past in it, and ㅆ furthers that) The important thing is that the adjective form for 갔다 is 간, not 갔던 as might appear correct to you. You can use either 갔던 or 갔었던 for #3, but 갔었던 with 었 gives the impression it was further in the past. So 갔었던 is often preferred for emphasis even though 갔던 carries almost the same meaning. Also, there is 가던 as well to complete the -던 forms: "-던" without the ㅆ 받침 indicate an action or state that recurred or lasted for a while in the past (like "used to"). - 내가 자주 가던 찻집: The cafe I used to frequent. - 내가 수행하던 프로젝트: The project I used to work on.

그가 갔던 마을 = the town he used to go to.(I'm not sure that he go to the town recently) 그가 갔었던 마을 = the town he had gone to.(I'm sure that he doesn't go to the town anymore) From http://www.howtostudykorean.com/unit-2-lower-intermediate-korean-grammar/unit-2-lessons-26-33/lesson-27/ ~ㄴ/은: Attached to a verb to describe a noun where the action occurred sometime in the past. There is no additional meaning given to it. All we know is that at some point in the past, the action happened. ~던: Attached to a verb to describe a noun where the action is recalled to have occurred repeatedly in the past, and continually repeating to the present (or to the time described in the sentence). ~았/었던: Attached to a verb to describe a noun where the action is recalled to have occurred in the past, but has finished occurring and currently does not occur. I don’t like distinguishing these grammatical principles based on their English translations. Given the number of possible situations that could come up, there is no perfect way to accurately translate any of them. However, the examples below show common translations for each of these grammatical principles in use: 내가 입은 바지 = the pants I wore 내가 입던 바지 = the pants I used to wear 내가 입었던 바지 = the pants I had worn.(I din't wear the pants anymore)