The RAID International Symposium series is intended to further progress in intrusion detection by promoting the exchange of ideas in a broad range of topics among researchers, system developers and users. RAID'98, held in Louvain-la-Neuve, Belgium, was hosted by the Universite Catholique de Louvain and welcomed 130 participants, with nearly 50% from outside Europe, reflecting the international nature of the meeting. RAID'99, held in Purdue, Indiana, was hosted by CERIAS and welcomed more than 180 participants from academia, government and industry.