Multi-Agent systems (Autonomous agents or agents) and knowledge discovery (or data mining) are two active areas in information technology. A profound insight of bringing these two communities together has unveiled a tremendous potential for new opportunities and wider applications through the synergy of agents and data mining. Multi-agent systems (MAS) often deal with complex applications that require distributed problem solving. In many applications the individual and collective behavior of the agents depends on the observed data from distributed data sources. Data mining technology has emerged, for identifying patterns and trends from large quantities of data. The increasing demand to scale up to massive data sets inherently distributed over a network with limited band width and computational resources available motivated the development of distributed data mining (DDM).Distributed data mining is originated from the need of mining over decentralized data sources. DDM is expected to perform partial analysis of data at individual sites and then to send the outcome as partial result to other sites where it sometimes required to be aggregated to the global result.