Random numbers are a fundamental part of science and technology, being especially relevant for cryptography, gaming, simulations or statistics. Quantum random number generators (QRNG) rely on the intrinsic randomness of quantum mechanics to generate true and unpredictable random numbers, unachievable from the classical physics perspective. Methods and protocols to certify and quantify the randomness in the output of a quantum system are a current subject of intensive research. In this thesis, we focus on the emergent field of quantum random number generation proposing two semidevice- independent schemes to harvest quantum entropy while discussing in detail their strengths and weaknesses. With the purpose of developing a certification protocol for these approaches, we thoroughly study the implementation of the photodetector and the possible vulnerabilities it might introduce in our approaches. Finally, we perform a proof-of-concept experiment to demonstrate the feasibility of the suggested schemes and experimentally investigate the correctness of the derived theoretical models. The results for these experiments revealed a satisfactory agreement with the theory and enabled us to extract 1.58 bits of quantum randomness per sample with an 8-bit digitisation out of our QRNG.