The Pharmacogenomics Knowledgebase (PharmGKB) is a resource that collects, curates, and disseminates information about the impact of human genetic variation on drug responses. It provides clinically relevant information, including dosing guidelines, annotated drug labels, and gene-drug associations. PharmGKB curators assign levels of evidence to variant-drug associations based on literature reviews. The knowledge base includes gene variant annotations, drug-centered pathways, and VIP summaries. Variant annotations are based on published articles and describe associations between genetic variants and drug phenotypes. Clinical annotations combine multiple variant annotations into a single summary of variant-drug-phenotype associations. For example, the TPMT*3B variant is associated with increased risk of side effects based on genotype. Each clinical annotation is linked to PubMed identifiers and contains a summary for each genotype. The level of evidence is determined by replication, P value, and odds ratio. Levels 1 and 2 are divided into A and B subtypes, with Level 1 involving strong evidence and Level 2 moderate evidence. Level 3 is based on a single study, and Level 4 on case reports or in vitro evidence. PharmGKB supports clinical implementation projects, such as the CPIC, which provides drug-dosing guidelines based on genotype. PharmGKB is a critical resource for enabling clinicians and researchers to implement pharmacogenomic knowledge in personalized medicine. The knowledge pyramid represents the hierarchy of PharmGKB knowledge, with clinical implementation at the top. PharmGKB welcomes input from the scientific and clinical community. All annotations are available in tab-delimited files after the Data Usage Agreement. The PharmGKB is supported by the National Institutes of Health.The Pharmacogenomics Knowledgebase (PharmGKB) is a resource that collects, curates, and disseminates information about the impact of human genetic variation on drug responses. It provides clinically relevant information, including dosing guidelines, annotated drug labels, and gene-drug associations. PharmGKB curators assign levels of evidence to variant-drug associations based on literature reviews. The knowledge base includes gene variant annotations, drug-centered pathways, and VIP summaries. Variant annotations are based on published articles and describe associations between genetic variants and drug phenotypes. Clinical annotations combine multiple variant annotations into a single summary of variant-drug-phenotype associations. For example, the TPMT*3B variant is associated with increased risk of side effects based on genotype. Each clinical annotation is linked to PubMed identifiers and contains a summary for each genotype. The level of evidence is determined by replication, P value, and odds ratio. Levels 1 and 2 are divided into A and B subtypes, with Level 1 involving strong evidence and Level 2 moderate evidence. Level 3 is based on a single study, and Level 4 on case reports or in vitro evidence. PharmGKB supports clinical implementation projects, such as the CPIC, which provides drug-dosing guidelines based on genotype. PharmGKB is a critical resource for enabling clinicians and researchers to implement pharmacogenomic knowledge in personalized medicine. The knowledge pyramid represents the hierarchy of PharmGKB knowledge, with clinical implementation at the top. PharmGKB welcomes input from the scientific and clinical community. All annotations are available in tab-delimited files after the Data Usage Agreement. The PharmGKB is supported by the National Institutes of Health.