Proteomics may be defined as the large-scale systematic study of the proteome – the complete set of proteins expressed by an organelle, cell, tissue, or organism at a certain time. Depending on the study type, either the top-down proteomics approach that analyzes intact proteins from biological systems, or the bottom-up approach that studies the proteins by analyzing the peptide fragments, could be used to obtain information on the target protein set. In a typical workflow, protein samples are collected, for example, from COVID-19 patients and healthy controls, and digested into peptides. Then, high-throughput techniques like MS, allow identification and comparative screening of significantly regulated or altered proteins between the study populations, which can be identified using available databases. This in-depth proteome profiling allows detection of disease-specific protein biomarkers and identification of potential therapeutic targets. Expression proteomics studies the differences in protein expression between samples. Structural proteomics helps map out the protein structure within a specific organelle, while functional proteomics identifies the biological functions of an individual or a class of proteins.