The security environment is undergoing rapid and constant change. Global security issues, such as terrorism and the related recruiting activities, widespread immigration, and cybercrime, exemplify the inseparability of internal and external security. The multifaceted cause-effect relationships and formation mechanisms of these issues, and the constantly morphing interaction, make operating in the security environment even more complex and forecasting its development more challenging. The development requires security actors to examine security in a wider scope, past actor-specific sector borders, and to cooperate more comprehensively and proactively. In order to respond to these developments, the Ministry of the Interior's strategic research project on the interdependence of internal and external security has established a more in-depth understanding of the inseparability of internal and external security, and produced development recommendations for improving the operational prerequisites and cooperation of the security actors. The project has been closely connected to the internal security strategy currently being prepared; the key perspectives and development recommendations produced during the project will be taken into consideration in the preparation process. The project implementation has been based on cross-administration cooperation between experts of the Ministry of the Interior and its sectors, the Ministry of Defence, and the Ministry for Foreign Affairs, utilising interviews and workshops. The International Affairs Unit of the Ministry of the Interior has acted as the responsible executor of the project. The five main levels of development jointly identified during the project process are: 1) development of the usability and shareability of information, 2) definition and shared interpretation of shared interests and goals concerning the security environment, 3) development of flexible cooperation models, 4) improvement of the flexibility of decision-making, and 5) improvement of the up-to-dateness and flexibility of the practices related to the definition of jurisdiction, and preparedness. Each main level includes a description of the development recommendations, the more detailed examination of which will be promoted as part of the preparation of the internal security strategy. The common goal of the development recommendations and the perspectives produced during the project is to promote the development of methods and operating models that better match the current security environment, and their establishment as part of the operational culture