Book excerpt: The field of Mitochondrial Medicine has been dominated by symptom constellation-based diagnostic categorization since the first clinical syndrome was described three decades ago. Now, as rapidly expanding knowledge has revealed that mitochondrial diseases may result from several hundred distinct gene disorders with extensive clinical and mutation heterogeneity, the most useful guide for clinical care and research embraces a gene-centric approach to each individual's disorder. Together with international colleagues, Dr. Marni Falk has developed the Mitochondrial Disease Sequence Data Resource (MSeqDR), an online, community curated, centralized data resource of mitochondrial disease data from a genomic perspective. Here, in the Mitochondrial Disease Genes Compendium, Dr. Marni Falk and a team of international experts have built off their work on MSeqDR to provide an all-in-one, readily accessible, and easy-to-use at point of care reference on 256 mitochondrial disease genes from a gene-based perspective. In this book, clinicians and researchers will find a complete overview of mitochondrial disease genes relevant across all specialties, cataloging and building context around clinical features and the genetic basis of each condition. Within, each "gene page" offers an in-depth, referenced view of the relevant clinical disease spectrum, including gene and protein descriptions, year discovered, inheritance pattern(s), age ranges affected, major clinical features and severity range, clinical pearls, known therapies, available support groups, animal models, and gene-specific basic, translational, or clinical research activities now underway. Links provided on each gene page direct readers to MSeqDR for new findings, up-to-date genomic variant data, and user friendly informatics tools accessible to general clinicians and sophisticated geneticists or bioinformaticians alike, ensuring access to updated information on each condition.