developed multiple open community data standards (e.g. mzML, mzidentML, mzTab), guidelines, and controlled vocabularies/ontologies, among other outputs, since its inception in 2002 . Here we describe the HUPO PSI mzSpecLib and mzPAF standards, designed to encode spectral libraries and annotations of peptide fragment ion peaks, respectively. They have been split into separate standards since fragment ion peaks may be annotated in contexts outside of spectral libraries, such as spectrum display software. However, they are described here together since they will most often be jointly used. We first provide an overview of the mzSpecLib format and then the mzPAF format, followed by descriptions of current software implementations that may guide further implementations.