This paper gives a review of the double beta experimental techniques and projects, in the search for the Majorana neutrino. The purpose of this review is to detail, for each technique, the different origins of background, how they can be identified, and how they can be reduced. Advantages and limitations of the different techniques are discussed. 1. Introduction The neutrino is one of the most puzzling elementary particle with very unique properties. It has no electrical charge 1 , it is thus only sensitive to weak interaction and its mass is very light. The absence of electrical charge is a major characteristic. Ettore Majorana showed that a neutral elementary particle which does not contain any discrete quantum number (as the neutrino), can be described by a so-called Majorana field, in which the distinction between matter and antimatter vanishes [2]. In other words, a neutrino might be identical to its own anti-particle. If the neutrino is a Majorana neutrino, an important consequence is that Lepton Number Violation (LNV) must occur [3][4]. LNV is a required condition for Grand Unified Theories (GUT), in which quarks and leptons are components of the same multiplet, and hence both lepton and baryon numbers are not expected to be conserved quantities. Leptogenesis is an example of model, which uses the LNV from the decay of heavy Majorana neutrinos to produce the observed asymetry of matter and antimatter in the Universe. Another motivation for the Majorana neutrino is the seesaw mechanism [5][3], which splits the Majorana mass term of neutrinos in light and heavy Majorana neutrinos and thus could explain the very small mass of the observed neutrinos, with the condition that the mass of the heavy one is at the GUT energy scale of about 10 15 GeV. The most sensitive method to answer the nature of the neutrino is the search of the neutrinoless double beta decay (ββ0ν).