Dementias correspond to a severe worldwide health problem, and it involves many symptoms. Dementias are characterized by an irreversible cognitive decline that affects mainly, but not exclusively, the memory. Dementias mainly affects elderly people, but it is not a normal consequence of aging. There are multiple imaging techniques that support the diagnosis of dementias: some are in clinical use, and other are research techniques. Magnetic resonance imaging standard protocols, visual assessment scales atrophy, cerebral volumetry techniques, fMRI paradigms, resting state functional connectivity, SPECT and PET are the techniques discussed in this article.