Peptide Spectral Library is a curated, annotated and non-redundant collection/database of LC-MS/MS peptide spectra. One essential utility of Peptide Spectral Library is to serve as consensus templates supporting the identification of peptide/proteins based on the correlation between the templates with experimental spectra. The process of peptide/protein identification is called spectral library searching. Comparing to traditional peptide spectra identification approach, sequence database searching, spectral library searching offers many unique benefits, which are illustrated in the following sessions.

Spectral library has been used in the small molecules mass spectra identification since 1980s. In the early year of shotgun proteomics, pioneer investigations suggested that similar approach might be appliable in shotgun proteomics for peptide/protein identification. But until recent years, with the availability of millions of confidently identified MS/MS spectra, the implementation of Peptide Spectral Library shows practical value.