This special issue of the International Journal of Numerical Methods for Heat and Fluid Flow comprises selected papers presented during the Eurotherm Seminar No 109 – Numerical Heat Transfer 2015. The conference was held on 27–30 September, 2015 in Warsaw, Poland and it was the 3rd conference in the series, following the previous meetings in Cracow (2005) and in Wroclaw (2012). Both the Scientific Committee Members and the Participants came from 17 countries.The special issue consists of twelve papers which have been selected to demonstrate an overview of the conference topics and to present few hot and important topics in numerical heat transfer.