Quantum key distribution (QKD) exploits the inherent strangeness of quantum mechanics to improve secure communication, enabling two pre-authenticated participants to establish symmetric encryption keys over long distances, without making any assumptions about the computational abilities of an adversary. QKD commonly relies on the transmission and detection of single photons to distribute the secret keys. but the secret-key generation rates are often limited by hardware, namely the ability to produce or detect nonclassical states of light. We address this challenge by using high-dimensional encoding to increase the secure information yield per detected photon. In this thesis, we present security analysis for and the first demonstrations of a resource-efficient high-dimensional QKD protocol. including two varieties of implementation that each have different strengths and weaknesses. We introduce a 42-km deployed fiber testbed that we use to demonstrate our high-dimensional QKD protocol. We also demonstrate the violation of a steering inequality, confirming that we can produce entanglement in the lab and distribute it over the deployed fiber. By these experiments. we demonstrate both the utility of our high-dimensional QKD protocol and the feasibility of our testbed for further applications in quantum communication and networking. (Copies available exclusively from MIT Libraries, libraries.mit.edu/docs - docs mit.edu).