Consciousness or conscious experience is a mental phenomenon that is familiar to all of us, but the way in which it is produced escapes us to a large extent. Each person has a vague idea of what it means to be conscious, but consciousness is rather hard to define, albeit easy to identify. It is that function of the brain that makes us conscious of external or internal stimuli and of our thoughts regarding these subjective experiences. Conscious experience is a first-person perspective of mental states and events tracking as they unfold. It includes mental phenomena such as a perception, emotion, memory, idea, continuous temporal sequence of events. A mental process and its adjoining neurophysiological phenomena represent two aspects of the same event. We have direct access to the mental aspect, while we can observe the neurophysiological aspect only when we study the event as a biological process. The psychological study of consciousness describes the special properties of this brain function, its origin and utility in the global economy of an animal organism. The neurobiological study aims to find the neural correlates of consciousness, aims to establish causal relations between the neural phenomena and the different conscious states. Lastly, the formulation of an explanatory theory can provide a satisfactory understanding of the phenomenon. This review aims to bring some clarification in the field of consciousness, selecting the hypotheses which mostly fulfill the requirements, in order to be confirmed as explanatory theories. A valuable test for confirming an explanatory hypothesis is its predictive power. Using this criterion we have evaluated comparatively, some of the proposed explaining hypotheses.