Random number generators are fundamental in several real-world applications, like cryptography and simulation. This need for randomness is commonly bridged using pseudo-random number generators, which rely on deterministic mathematical algorithms to produce uniform random sequences. It is not rare to find situations in which the deterministic aspect of these objects is not acceptable. To make up for this need, true random number generators can be used, in particular Quantum Random Number Generators (QRNGs), that exploit the inherently random nature of quantum mechanical phenomena to generate numbers. Several paradigms of QRNGs are possible, regarding the elements of the system that can be considered as trusted.