This issue of "Leadership and Policy in Schools" outlines research into successful principal leadership from the perspective of four countries--New Zealand, Israel, Cyprus, and the USA (San Antonio). The research followed the methods and protocols established by the International Successful School Principalship Project (ISSPP), which was established in 2001 to examine the characteristics and practices used by successful school principals across countries. Each of these countries joined the ISSPP in 2007. Their research follows phase one of the ISSPP research agenda--multiple perspective case studies of successful school principals. The inaugural group of the ISSPP comprised research teams from Australia, Canada, China, England, Denmark, Norway, Sweden, and the USA (Buffalo, New York). This article summarizes the accumulated findings from the 63 case studies from these founding groups, and then evaluates the contribution of the new case studies to the ISSPP.