Korea and Japan are the two leading countries designing and building up-to-date nuclear power plants in world. In the hopes to contribute the nuclear system performance with enhanced safety, the thermal-hydraulics and nuclear safety divisions of the KNS and the AESJ initiated a biennial symposium program across the sea: Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS). Since the first symposium (NTHAS-1) in Busan, Korea in 1998, NTHAS has provided a unique opportunity to discuss up-to-date technical information and to interact with colleagues from the neighboring countries. The second to tenth meetings were held in Fukuoka (2000), Gyeongju (2002), Sapporo (2004), Jeju (2006), Okinawa (2008), Chuncheon (2010), Beppu (2012), Buyeo (2014) and Kyoto (2016) with great success in technical quality and number of participants. This year, the 11th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-11) will be held in Busan, Korea. The official language of the symposium is English.