In multi-national and multi-functional contexts, the Swedish Armed Forces need to interact with other nations´ armed forces and civilian organizations (e.g. the police). The demand for collaborative ability is, of course, also relevant from a national perspective, where the armed forces need to interact with other organisations and across different command and control systems. It is therefore of great importance that command and control systems are developed with flexibility in mind, in order to be able to adapt to different situations in which the need to exchange information between systems exists. To ensure conformity with international requirements (NATO/EDA), development must be carried out in collaboration with international projects and initiatives. Within NATO, semantic interoperability (SI) has been identified as a core capability for future command and control systems. Two actors that are semantically interoperable can not only exchange information, but can also interpret and understand the intended meaning of the information in a common way. This is a key issue in the interaction between groups that do not share common frames of reference acquired through a common culture or through education. Support for semantic interoperability is therefore a prerequisite for the ability to participate in international operations with allied forces. The value of this research, in the long term, is an assured semantic interoperability that makes the implementation of multi-national operations more efficient. Semantic interoperability may contribute to various capabilities of the armed forces, but is above all expected to increase the safety of international operations. Despite this, semantic interoperability has not yet been identified as a requirement for information exchange between different systems. Problems related to the use of different data formats, or pure connectivity issues, all too often distract from what is really the main problem - to understand and interpret information in a consistent manner. Especially where information exchange is taking place between multiple domains, the importance of this aspect cannot be emphasized enough. Semantic interoperability aims to achieve a common understanding of one or more domains, before the exchange of operational information between systems take place. Since current development processes do not take into account the preservation of the intended meaning of concepts in the exchange of information, any attempt to integrate heterogeneous systems for multi-national operations without taking semantic interoperability into consideration will necessarily be insufficient. Traditionally, each domain has developed and managed their own systems and data formats. This has resulted in organisational silos and thus, the exchange of information between different domains has become very difficult to realise (sometimes even difficult for systems within the same domain). This represents a major challenge for all operational contexts within which information must be shared among different domains and systems. The traditional means of exchanging information between systems do not provide the opportunity to understand and share the intended meaning of information (the semantics). To enable this, an architecture, encompassing a common or agreed upon terminology (ontology) and developed and maintained using formal methods, is needed. Such an ontology is implicit among a group of people exchanging messages (otherwise the communication would be impossible), but in this architecture it is made explicit. This allows every message between communicating actors to include references to one or several ontologies according to which the message is interpreted. This report provides an introduction to the problem of semantic interoperability within the Swedish Armed Forces, and also addresses the problem from an international perspective. The various levels of interoperability are discussed and it is concluded that a solution for semantic interoperability should involve the use of ontologies (i.e. knowledge-based semantic interoperability). Thus, the notion of ontology is explained, along with how it could be utilized from the perspective of semantic interoperability. Given this background, a general logical framework for semantic interoperability, SILF (Semantic Interoperability Logical Framework) is introduced. In connection with the introduction of SILF, the conditions necessary for it to function efficiently are discussed. Thereafter, a comparison is made between SILF and existing standards in the field of distributed simulation, an area which has also struggled with similar issues for many years. Finally, an overview of currently available techniques and tools that are of interest in realizing SILF and are related to semantic techniques and ontologies, is presented. The most important conclusion of the report is that future systems must have the ability to describe their external interfaces, either in terms of ontologies or in other equivalent formal formats. The reason is simply that otherwise these systems will most likely not be useful in future multinational operations, despite the fact that such a direction is clearly desired by the Swedish Armed Forces. Based on this conclusion, the most important recommendation covered by the report is, that all the procurement officers ordering systems, such as FMV handling officers, must already today require such formal descriptions in the context of their orders.