## 1 Introduction  
Carotenoids are pigments that have received considerable attention due to their biotechnological applications and, more importantly, their potential beneficial effects on human health [1; 2; 3]. These compounds are the second most abundant naturally occurring pigments in nature [4], and they are mainly C\({}_{40}\) lipophilic isoprenoids ranging from colourless to yellow, orange, and red [5]. The production of such as kind of pigment has been described from plants and some microorganisms such as algae, cyanobacteria, yeast [6] and fungi [7; 8].  
Plants, algae, yeast, cyanobacteria and fungi have been considered good sources to isolate and even to produce carotenoids at high scale so far [9; 10; 11; 12]. In fact, general characterisations of carotenoids isolated from those organisms are abundant in the literature, in which techniques such as spectrophotometry, thin layer chromatography (TLC), high performance liquid chromatography-mass spectrometry (HPLC-MS) and nuclear magnetic resonance spectroscopy (NMR) are used to define the carotenoids profile from specific species as well as the carotenoids chemical structure [13; 14; 15; 16; 17; 18]. However, not too much attention has been paid to halophilic microorganisms, and in particular, to haloarchae as microorganisms with high capability of carotenoids production.  
Halophiles comprise a heterogeneous group of microorganisms that require salts for optimal growth. Even high salt concentration up to 4 M is required for some extremophilic species such those belonging the _Haloferacaceae_ family, Archaea domain. The pigments produced by these halophilic organisms include phytoene, \(\beta\)-carotene, lycopene, derivatives of bacterioruberin, and salinixanthin [19]. _Dunaliella salina_ is one of the better known halophilic microorganisms in terms of carotenoids production [20; 21; 22; 23]. However, apart from that halophilic microalgae, only few studies have been carried out about production of carotenoids by halophiles and in most of the cases, the studies are focused on carotenoids isolation and characterisation by traditional biochemical procedures as those mentioned before [24; 25; 26].  
Within the halophiles there is a family of particular interest in several fields of applications: micro-ecology, biotechnology and extreme metabolic adaptations. This is the case of the _Haloferacaceae_ family (previously mentioned) grouping extreme halophilic archaea inhabiting salty environments such as marshes or salty ponds from where NaCl is obtained for human consumption [27; 28; 29; 30]. The first study about carotenoid production by halophilic microorganisms from the _Haloferacaceae_ family (previously called _Halobacteriaceae_ family) were published in the latter half of the 1960s [31; 32]. During the last two decades of the last century, several research works demonstrated that some haloarchaeal species not only produce carotenoids but also produce them at high concentration. This fact makes possible to propose haloarchae as a good natural source for carotenoids production at large scale by means of suitable bioprocess engineering tools, namely specifically designed bioreactors.  
This review summarised what it has been described up to now about carotenoids production by haloarchae and its potential uses in Biotechnology and Biomedicine. The effect of different parameterson carotenogenesis in haloarchaea such as temperature, salt concentration, pH and carbon/nitrogen ration is also discussed.