PhosphoSitePlus (PSP), a database of mammalian post-translational modifications (PTMs), has expanded significantly since 2003, now containing over 330,000 non-redundant PTMs, including phospho, acetyl, ubiquityl, and methyl groups. Over 95% of these sites are derived from mass spectrometry (MS) experiments. To improve data reliability, early MS data have been reanalyzed using a common standard across over 1 million spectra, filtering out site assignments with P > 0.05. Two new datasets, 'Regulatory sites' and 'PTMVar', have been introduced. 'Regulatory sites' provide curated information on modification sites regulating cellular processes, while 'PTMVar' identifies over 25,000 PTMVars (PTMs impacted by variants) that can rewire signaling pathways. These include missense mutations from UniPROTKB, TCGA, and other sources linked to over 2000 diseases or syndromes. PSP now contains 18,548 phosphorylation sites, 3,412 ubiquitylation sites, 2,316 acetylation sites, 685 methylation sites, and 245 succinylation sites. PSP has grown from 128,943 modification sites in 2003 to 338,948 in 2014, with 274,396 sites on 20,021 human proteins, 139,066 on 15,389 mouse proteins, and 42,465 on 7,204 rat proteins. The database now hosts 1.5 million peptides and has improved data quality by reprocessing older data with updated algorithms. The 'PTMVar' dataset maps missense mutations to PTM sequence space, aiding in understanding disease mutations and genetic risks. PSP also includes kinase-substrate interactions (KSIs) and sequence logos for kinase specificity. The database has expanded its sequence space to include UniPROT SwissProt sequences, improving data stability. PSP now includes chromosomal locations for human proteins and links to other resources like the Human Protein Atlas and BioGPS. PSP offers two types of downloads: interactive search results and static datasets. The 'PTMVar' dataset includes 17,551 modification sites associated with 24,592 mutations, with 39% classified as disease mutations, 44% as polymorphisms, and 17% as unclassified. The 'Regulatory sites' dataset includes 7,211 sites on 2,374 proteins regulating cellular processes, molecular functions, and protein-protein interactions. The 'Kinase Substrate'PhosphoSitePlus (PSP), a database of mammalian post-translational modifications (PTMs), has expanded significantly since 2003, now containing over 330,000 non-redundant PTMs, including phospho, acetyl, ubiquityl, and methyl groups. Over 95% of these sites are derived from mass spectrometry (MS) experiments. To improve data reliability, early MS data have been reanalyzed using a common standard across over 1 million spectra, filtering out site assignments with P > 0.05. Two new datasets, 'Regulatory sites' and 'PTMVar', have been introduced. 'Regulatory sites' provide curated information on modification sites regulating cellular processes, while 'PTMVar' identifies over 25,000 PTMVars (PTMs impacted by variants) that can rewire signaling pathways. These include missense mutations from UniPROTKB, TCGA, and other sources linked to over 2000 diseases or syndromes. PSP now contains 18,548 phosphorylation sites, 3,412 ubiquitylation sites, 2,316 acetylation sites, 685 methylation sites, and 245 succinylation sites. PSP has grown from 128,943 modification sites in 2003 to 338,948 in 2014, with 274,396 sites on 20,021 human proteins, 139,066 on 15,389 mouse proteins, and 42,465 on 7,204 rat proteins. The database now hosts 1.5 million peptides and has improved data quality by reprocessing older data with updated algorithms. The 'PTMVar' dataset maps missense mutations to PTM sequence space, aiding in understanding disease mutations and genetic risks. PSP also includes kinase-substrate interactions (KSIs) and sequence logos for kinase specificity. The database has expanded its sequence space to include UniPROT SwissProt sequences, improving data stability. PSP now includes chromosomal locations for human proteins and links to other resources like the Human Protein Atlas and BioGPS. PSP offers two types of downloads: interactive search results and static datasets. The 'PTMVar' dataset includes 17,551 modification sites associated with 24,592 mutations, with 39% classified as disease mutations, 44% as polymorphisms, and 17% as unclassified. The 'Regulatory sites' dataset includes 7,211 sites on 2,374 proteins regulating cellular processes, molecular functions, and protein-protein interactions. The 'Kinase Substrate'