Basic proteomic data acquisition involved protein separation, digestion, and peptide mass fingerprinting to identify the proteins. This chapter outlines the main types of protein mass spectrometry in the context of peptide mass fingerprinting. It offers a detailed explanation of charge deconvolution for computing the molecular mass from the distribution of multiple charged ions of the molecule of interest. Once we obtain a list of peptides with computed peptide mass, we can search them against a set of in silico digested peptides for matches. Statistical methods for identifying proteins from such matches are presented, together with an example of sloppy thinking leading to spurious correlation between variables relevant to protein crystallography.