In this chapter we briefly review present implementations of single-photon and photon-pair sources. After providing the basic fundamentals of nonclassical light, the role of photon detection to characterize these sources is highlighted. Then, we motivate why ongoing experiments heading at the realization of more complex quantum optical devices make very high demands on detectors and detection electronics. First, results towards quantum repeater architectures and hybrid quantum systems are discussed. Finally, we outline future prospects of all-optical quantum technologies.