Photonic quantum technologies are a promising approach to implement quantum information tasks including physically secured communication, efficient simulation of quantum systems, and could ultimately lead to the realisation of a full scale quantum computer. Integrated photonics have been successfully used to expand the scope of quantum optics experiments, unlocking the capability to perform more and more complex quantum tasks. The current effort points towards the integration of all the components in a single monolithic chip including single photon sources, passive circuits, fast phase-modulators, single photon detectors and electronics. Following this goal, we present technological steps towards further integration. We first show fast manipulation of single and two-photon states in an integrated lithium niobate circuit. We then move to the silicon-on-insulator platform providing orders of magnitude more compact circuits. We demonstrate the operation of several key components in the quantum regime, including quantum interference in a passive integrated multimode coupler, manipulation of quantum states using a reconfigurable phase-shifter in a Mach-Zehnder interferometer, and on-chip production of photon pairs. Engineering considerations are discussed for different components, including a study of the optimal parameter space for resonant photon pair sources. We then demonstrate the combined operation in a single chip of two photon pair sources together with passive circuitry and a phase-shifter, and show high visibility on the resulting quantum interference fringes. Then, considering state of the art technologies, including results from this work, we study several multiplexed schemes for implementing a crucially missing building block so far: a near-deterministic single photon source.