Intelligence organizations and their operations are by their nature secretive and want to continue as such. This problematizes research around them and especially intelligence cooperation with other countries can be considered among the most secret parts of an intelligence organization. This is put in the context of the essay where Sweden and Finland have a long and extensive historical relationship. That relationship also includes military aspects with volunteer soldiers and even today with the joint decision to apply to NATO. Previous research on Swedish intelligence gathering and intelligence cooperation in Finland has been sparse and scattered in larger works that have focused largely on the Swedish intelligence organization and its operations. The purpose of the essay is twofold. One is to map the Swedish intelligence gathering in Finland by C-byrån and see how it changed during the course of the war. The second is to highlight and discuss the intelligence cooperation between the Swedish and Finnish intelligence services. Since the purpose is twofold, two different theoretical frameworks and researchers' thoughts will be used. The first is Agrell's thoughts on different types of intelligence, which will be used to analyze what is obtained in Finland. The second is Michael Herman's thoughts on intelligence cooperation, which will be used to explain and discuss the Swedish-Finnish intelligence cooperation. The method chosen for this essay is a qualitative text analysis with a close reading of reports carried out. The essay will also contain elements of quantitative methods in the form of a table and figures to more easily visualize some of the results. The end result of this essay is that the C-byråns intelligence gathering in Finland changed in volume and type of intelligence during the course of the war. Within the intelligence cooperation, it is established that the cooperation was at its greatest and in clarity during the Finnish Winter War. After the Finnish Winter War cooperation decreased and became discreet, then returned during the Lapland War in clarity. Intelligence cooperation with the Finnish intelligence service became a method of approach and a professional exchange for the C-byrån to obtain intelligence on active war experience of how Soviet troops fight and their tactics.