In the last few years, vaccine hesitancy has considerably grown in the populations of western countries, particularly since controversies about the utility and safety of vaccines and their adjuvants recently multiplied. After a critical examination of the concept of " vaccine hesitancy " as well as its expressions through history, we will address the main psychological and sociological processes that could help us to better understand its development in modern societies. On the one hand, the evidence drawn from the existing literature shows that vaccine hesitancy typically derives from an intuitive trade-off between the perceived risks and benefits from the vaccination. Nevertheless, these perceptions have been repeatedly found to be prone to various cognitive biases. On the other hand, two sociological trends enable us to explain the proliferation of controversies about vaccines. Thefirst stems from a growing feeling of distrust toward government institutions in general and the public health authorities in particular. The second comes from the radical evolution of the news " market " which is caused by the development of electronic media. The combination of these two phenomena facilitates the rapid propagation of a variety of rumors, and incorrect or suspicious information, which are likely to affect the acceptance of vaccines.