Thermophotovoltaic (TPV) device converts thermal radiation into electricity output through photovoltaic effect. High-efficiency TPV devices have extensive applications in grid-scale thermal storage, full-spectrum solar utilization, distributed thermal-electricity cogeneration, and waste heat recovery. The key to high-efficiency TPV devices lies in spectral regulation to achieve band-matching between thermal radiation of the emitters and electron transition of the photovoltaic cells. The latest advances in nanophotonics, materials science, and artificial intelligence have made milestone progress in spectral regulation and recording power conversion efficiency of up to 40% of TPV devices. Here we systematically review spectral regulation in TPV devices at the emitter end as well as the photovoltaic cell end. At the emitter end, spectral regulation is realized through thermal metamaterials and rare-earth intrinsic emitters to selectively enhance the in-band radiation and suppress the sub-bandgap radiation. At the photovoltaic cell end, spectral regulation mainly focuses on recycling the sub-bandgap thermal radiation through optical filters and back surface reflectors located at the front and back of the photovoltaic cells, respectively. We emphasize the light-matter interaction mechanisms and material systems of different spectral regulation strategies. We also discuss the spectral regulation strategies in near-field TPV devices. Finally, we look forward to potential development paths and prospects of spectral regulation to achieve scalable deployment of future TPV devices.