In this talk I present the evolution of physical random number generators (RNGs). I start by explaining the uses of RNGs and their desired characteristics. Then I discuss physical processes used to generate random numbers and the influence of the chosen process on properties of the randomness obtained. Classical RNGs, that is devices which behaviour is described without resorting to quantum mechanics, are covered only briefly. Most of the talk is devoted to quantum devices and special attention is devoted to recent efforts on producing RNGs which can self-certify the parameters of randomness generated.