Abstract: The disclosure provides nicotinamide riboside (NR), the reduced form of NR (NRH), nicotinic acid riboside (NAR), the reduced form of NAR (NARH), derivatives thereof, compositions thereof and uses thereof. The NR and NAR derivatives have improved stability and bioavailability compared to NR and NAR. NR, NRH, NAR, NARH, and derivatives thereof can increase intracellular NAD+ levels, and can enhance mitochondrial and cellular function and cell viability. Therefore, NR, NRH, NAR, NARH, and derivatives thereof, whether alone or in combination with one or more additional therapeutic agents (e.g., a PARP inhibitor), are useful for treating mitochondrial diseases, mitochondria-related diseases and conditions, and other disorders and conditions.