Research Context: The internet has become an indispensable tool in today's society. However, data transfer over this network is fundamentally insecure. Security of data and protection against identity theft and cyber-attacks is of crucial importance for our current and future society. These security concerns are addressed with the invention of a quantum internet - a network based on encoding and transmitting information as quantum bits - as the principles of quantum physics ensure total and fundamental secure communication. Quantum networks are the missing key technology, however, a major roadblock remains to be overcome: scalability. Building quantum networks relies on generating large numbers of individual quantum objects (in this case photons - single quanta of light) and performing controlled interactions between them. However, the fragile nature of quantum objects means that successfully preparing even one happens by chance - like a coin toss. Adding more quantum objects to a network is like adding more coins to toss - the overall chance of getting all heads reduces greatly, and so a large-scale quantum network has never been achieved. I will address this crucial issue with a quantum optical memory - a device that can store and recall photons on demand enabling one to synchronise the successful "coin tosses" across the network. The overall aim is to build and exploit a high-performance light-matter quantum network. Aims/Objectives: To achieve this aim, I will utilise my expertise in quantum light-matter interactions to build an ultrafast, high-efficiency, low-noise quantum memory at wavelengths already used in the telecoms industry. I will utilise two complementary platforms with miniaturisation capability important for scale - warm alkali vapours and cryogenically cooled rare-earth ions in solids - together with quantum memory protocols that I have pioneered, to deliver a quantum memory performance at an unprecedented level. With this device, I will demonstrate a hybridised quantum light-matter interface with the storage and on-demand recall of photons ensuring that the quantum properties of the light are preserved. This demonstration forms the key technology for the basis of the network, where I will now use two quantum memories to efficiently interface and store photons from disparate quantum sources at remote locations - a two-node network. I will then scale this light-matter network to allow for the control of multiple memories and photons to enact quantum communication tasks for the first-time. Potential Applications: In the same way the invention of the transistor led to rapid advances in computation and communications, revolutionising the 20th century, quantum networks are the underpinning technology that have the potential to bring significant change and long-term social-economic impact in the 21st century. A high-performance light-matter quantum network will bring inherently secure communication, more accurate global clock synchronization for enhanced GPS accuracy, and could even allow extending the baselines of telescopes for improved observations. Networks of quantum objects can form quantum computers that are powerful enough to solve problems that current computers cannot, with the potential to impact methods of research in the healthcare, pharmaceutical and green energy sectors. Efficient simulation and optimised computation using quantum networks could provide benefits in epidemiology and genetic research, cut costs in medication design to treat new diseases, and help improve artificial light-harvesting devices for alternative energy sources, with many more useful applications likely to be discovered in the coming decades. In the shorter term, my project will aid in training the next generation of quantum scientists and generate valuable IP to be exploited by spinout companies, further forwarding the emergent quantum technologies industry in the UK.