The aim of the Iceland Deep Drilling Projects (IDDP) was to drill to a depth of 4-5 km in known high-temperature areas to investigate their roots. The paper describes the design of the "generic" IDDP well and what the plans were. The challenges are to drill a large well with five cemented casing strings to 4500 m into a reservoir which can have a temperature of 400-600 C. In 2009 well IDDP-1 was drilled according to these plans but could not reach below 2100m due to the intersection of magma, as will be described in other papers in this special issue of Geothermics. The paper is thus for the historical record of the original design premises and intentions. (C) 2013 Elsevier Ltd. All rights reserved.