While Rishimishra's definitions are correct, they don't answer your question properly. Btw, in his second answer, to be more clear, I would refer to the situation as an experience. So, depending on the context, both of these ARE correct and they can both mean that this is an action that started in the past and is still continuing. The biggest difference between these two is that "have been living" suggests that they will continue living here. It's because you are using "for" in your first tense (present perfect), that these two have the same meaning. If you only said "They have lived in London", it is possible that they still live there, but we don't know for sure. With the continuouse tense, we know they still live there. And to properly confuse you, here's a slightly advanced tip: by using the second tense (present perfect continuous) it sounds like you are implying that this is a temporary situation: they are living in London now but for example they will move somewhere else when his contract expires in two years.

You can use the present perfect to talk about a place, city or country you have visited or travelled to. The present perfect is used to talk about IF, at any point in your life in the past, you have visited or travelled to a specific place. The present perfect is NOT used to talk about WHEN you did something. It is used to talk about IF you did something!

They have been living in London for 2 years because they are currently living there and process is still learning that's why we use present perfect continuous tense .

1. "They have lived in London for two years" means they lived in London, but it is not clear when did they live there. May be from 1945 to 1947. 1. "They have been living in London for 2 years" means they are still living in London and If the statement is made recently, then they have been living there since 2012.