Since the discovery of Hendra virus in Australia in 1994, bats have been implicated as an important reservoir of many high profile emerging zoonotic viruses including Nipah, SARS, MERS, Marburg and Ebola viruses. Several studies have recently demonstrated that bats are special as virus reservoir in two aspects: 1) they harbour more viruses than any other mammalian order (including rodents); and 2) they are able to co-exist asymptomatically with a large number of different viruses, some of which are highly lethal in other mammalian hosts. Our group has been researching into the question on “what makes bats special?” and made several discoveries which may help to explain bats’ special ability to maintain an effective balance between defence/resistance and tolerance. We hypothesize that their special ability to response to stresses (such as DNA damage and infection) is driven by bats’ adaptation to flight since their divergence from land mammals approximately 100 million years ago. A brief review of our latest findings will be presented in the context of immune balance and viral infections.