Single-cell proteomics has emerged as a revolutionary domain in biomedical research, facilitating the precise analysis of cellular heterogeneity at the protein level. Recent technological advancements—such as ultra-sensitive mass spectrometry, microfluidic sample preparation, and multiplexed labeling techniques—have markedly improved the depth, throughput, and reproducibility of single-cell protein quantification. These improvements have facilitated novel understandings of cell-state dynamics, lineage trajectories, and post-translational alterations that were previously concealed in bulk analysis. This chapter offers a thorough examination of recent methodological advancements in single-cell proteomics, encompassing label-free and isobaric tagging techniques, data-independent acquisition (DIA), and novel spatial proteomics platforms. It additionally investigates integrative frameworks that amalgamate single-cell proteomics with transcriptomics and epigenomics to create multidimensional cellular atlases. Applications encompass various fields including cancer biology, immunology, neurodegeneration, and regenerative medicine, where single-cell proteome profiling is revealing new biomarkers, therapeutic targets, and mechanisms of disease development. This chapter emphasizes the significance of single-cell proteomics in enhancing precision medicine and systems biology by showcasing its present capabilities and future trajectories.