The purpose of this thesis was to find out what kind of different forms of cooperation the public libraries and adult education centers have for each other. There were five different libraries targeted at the study's interviews. Interviews were used to find out what kind of forms of cooperation libraries and adult education centers have, whether the co-operation was good or bad and whether there is anything to be developed or improved. The libraries I selected for the interviews were from Eastern Finland, because I am from the area and from there it was easy to visit on the spot in almost all locations to conduct the interview. I used qualitative research method because there were not so many research targets in the study. There have also been no more in-depth studies in the past so such a research method seemed appropriate. In the study it was found out that the co-operation has been a good thing for example in planning different events and on both sides to increase visibility for customers. The study showed that the most common form of co-operation in the public library and at the adult education center is the use of facilities in joint action. The study also found that, in some cases, some of the library's staff may or may have worked at the adult education center. The problems of cooperation were noted, among other things, that some of the adult education center courses are chargeable and therefore cannot be arranged in libraries. Finally I think about how the co-operation could develop and what kind of issues the public libraries and adult education center could concentrate on.