Complex neurobiology of post-traumatic stress disorder (PTSD) is still unclear; however, its development is influenced by both environmental and genetic factors. Previous research aiming to identify potential genetic markers of PTSD mostly relied on its neurobiological background and various association studies targeted variations in candidate genes, usually coding for enzymes, receptors, ion channels, or transporters, involved in neurotransmitter, neurotrophic and immune systems, hypothalamic–pituitary– adrenal (HPA) axis, as well as for proteins related to neuronal and synaptic function. However, despite significant amount of data, our understanding of polygenic underpinnings of PTSD is still limited, partly due to inconsistent results. Therefore, larger candidate gene studies should be combined with findings obtained by molecular biological and animal research, assessing alterations in biochemistry, neural connectivity and behavior.