Recent advances in this understanding of light-matter interactions, combined with innovations in the design and fabrication of large-scale nanostructured metasurfaces, have enabled transformative approaches to biosensing and bioimaging. This review delves into the profound impact of optical metasurfaces, highlighting innovations that leverage their tunable properties and adaptability. It begins with an overview of key sensing mechanisms across various metasurface modalities, comparing their effects on metrics such as sensitivity and limits of detection. The discussion then shifts to recent advancements in refractometric biosensing, focusing on novel transduction methods that exploit the intensity, phase, and colorimetric responses of these metasurfaces. The latest developments in surface-enhanced spectroscopic sensing are also examined, exploring how metasurfaces contribute to enhanced molecular fingerprinting capabilities in these applications. Additionally, the role of optical metasurfaces in advancing bioimaging are assessed, emphasizing label-free elastic scattering, spectroscopic/chemical contrast imaging, and metasurface-assisted super-resolution microscopy. Finally, the review addresses current challenges and future directions for optical metasurfaces in biosensing and imaging, including material limitations, difficulties in large-scale fabrication, and the complexity of data analysis and readout methods. It also discusses the integration of novel detector hardware to improve spatiotemporal resolution of sensing and imaging techniques.