Within the future Global Information Grid, complex massively interconnected systems, isolated defense vehicles, sensors and effectors, and infrastructures and systems demanding extremely low failure rates, to which human security operators cannot have an easy access and cannot deliver fast enough reactions to cyber-attacks, need an active, autonomous and intelligent cyber defense. Multi Agent Systems for Cyber Defense may provide an answer to this requirement. This paper presents the concept and architecture of an Autonomous Intelligent Cyber defense Agent (AICA). First, we describe the rationale of the AICA concept. Secondly, we explain the methodology and purpose that drive the definition of the AICA Reference Architecture (AICARA) by NATO's IST-152 Research and Technology Group. Thirdly, we review some of the main features and challenges of Multi Autonomous Intelligent Cyber defense Agent (MAICA). Fourthly, we depict the initially assumed AICA Reference Architecture. Then we present one of our preliminary research issues, assumptions and ideas. Finally, we present the future lines of research that will help develop and test the AICA / MAICA concept.