Artificial immune systems (AIS) are still considered in an infancy stage by most of the practitioners in computational intelligence (CI). The AIS methods build adaptive large-scale multi-agent systems that are open to the environment, systems that are not at all fixed just after the design phase, but are real-time adaptive to unpredictable situations and malicious defects. The AIS perform the defence of a complex system against malicious defects achieving its survival strategy by extension of the concept of organization of multicellular organisms to the information systems. The main behavioural features of AIS - as self-maintenance, distributed and adaptive computational systems - are defined and described in relation to the immune system as an information system. AIS methodology is compared with other Intelligent Technologies. The overview of some actual AIS applications is made using a practical engineering design strategy that views AIS as the effective software with agent-based architecture.