In this Technical Design Report (TDR) we describe the NEXT-100 detector that will search for neutrinoless double beta decay (ßß0v) in 136XE at the Laboratorio Subterráneo de Canfranc (LSC), in Spain. The document formalizes the design presented in our Conceptual Design Report (CDR): an electroluminescence time projection chamber, with separate readout planes for calorimetry and tracking, located, respectively, behind cathode and anode. The detector is designed to hold a maximum of about 150 kg of xenon at 15 bar, or 100 kg at 10 bar. This option builds in the capability to increase the total isotope mass by 50% while keeping the operating pressure at a manageable level. The readout plane performing the energy measurement is composed of Hamamatsu R11410-10 photomultipliers, specially designed for operation in low-background, xenon-based detectors. Each individual PMT will be isolated from the gas by an individual, pressure resistant enclosure and will be coupled to the sensitive volume through a sapphire window. The tracking plane consists in an array of Hamamatsu S10362-11-050P MPPCs used as tracking pixels. They will be arranged in square boards holding 64 sensors (8 x 8) with a 1-cm pitch. The inner walls of the TPC, the sapphire windows and the boards holding the MPPCs will be coated with tetraphenyl butadiene (TPB), a wavelength shifter, to improve the light collection. © 2012 IOP Publishing Ltd and Sissa Medialab srl. ; Spanish Ministerio de Economia y Competitividad [CSD2008-0037 (CUP), FPA2009-13697-C04-04, RYC-2008-03169] ; Portuguese Foundation for Science and Technology [PTDC/FIS/112272/2009] ; European Commission under the European Research Council of the IDEAS program of the 7th EU Framework Program [ERC-2009-StG-240054 (T-REX)] ; Office of Science, Office of Basic Energy Sciences, of the US Department of Energy [DE-AC02-05CH11231] ; US DOE NNSA [DE-FC52-08NA28752] ; Alvarez, V.; Borges, F. I. G. M.; Carcel, S.; et ál. (2012). NEXT-100 Technical Design Report (TDR). Executive summary. Journal of Instrumentation. 7(6):1-34. doi:10.1088/1748-0221/7/06/T06001. ; Senia ; 1 ; 34 ; 7 ; 6