Mitochondria are ancient endomembrane systems in eukaryotic cells, essential for ATP production and evolution. Their genome, reduced from a bacterial ancestor, is now small and circular, with 16 kb, and is present in large numbers in human cells. Mitochondria produce ATP through the respiratory chain, creating an electrochemical gradient that powers ATP synthase. They also regulate Ca²+ levels and are involved in various cellular functions. Mitochondria contain over 1,000 proteins, a mix of bacterial and eukaryotic origins, and their genome encodes 22 tRNAs and 2 rRNAs. The mitochondrial proteome is regulated by nuclear genes, with PGC-1 co-activators controlling biogenesis. Mutations in mtDNA or nuclear genes cause mitochondrial diseases, with heteroplasmy contributing to disease severity. Mitochondrial dysfunction is linked to aging and various diseases. Mitochondrial DNA is packaged into nucleoids, regulated by TFAM and other proteins. mtDNA segregation is stochastic, with a bottleneck in oocytes and iPS cells. Mitochondrial dynamics, mediated by dynamin-related proteins, involve fusion and division, crucial for distribution and function. ER-associated mitochondrial division (ERMD) is regulated by the ER and involves the ERMES complex. Mitochondrial division is controlled by DRPs, with ERMD ensuring proper mtDNA distribution. Mitochondrial quality control pathways, such as UPRmt and mitophagy, respond to dysfunction, with PINK1-Parkin mediating mitophagy. These pathways are important for disease and aging. Mitochondrial organization and function are complex, with structural and functional domains essential for cellular needs. Advances in research are improving understanding of mitochondrial biology and its role in disease.Mitochondria are ancient endomembrane systems in eukaryotic cells, essential for ATP production and evolution. Their genome, reduced from a bacterial ancestor, is now small and circular, with 16 kb, and is present in large numbers in human cells. Mitochondria produce ATP through the respiratory chain, creating an electrochemical gradient that powers ATP synthase. They also regulate Ca²+ levels and are involved in various cellular functions. Mitochondria contain over 1,000 proteins, a mix of bacterial and eukaryotic origins, and their genome encodes 22 tRNAs and 2 rRNAs. The mitochondrial proteome is regulated by nuclear genes, with PGC-1 co-activators controlling biogenesis. Mutations in mtDNA or nuclear genes cause mitochondrial diseases, with heteroplasmy contributing to disease severity. Mitochondrial dysfunction is linked to aging and various diseases. Mitochondrial DNA is packaged into nucleoids, regulated by TFAM and other proteins. mtDNA segregation is stochastic, with a bottleneck in oocytes and iPS cells. Mitochondrial dynamics, mediated by dynamin-related proteins, involve fusion and division, crucial for distribution and function. ER-associated mitochondrial division (ERMD) is regulated by the ER and involves the ERMES complex. Mitochondrial division is controlled by DRPs, with ERMD ensuring proper mtDNA distribution. Mitochondrial quality control pathways, such as UPRmt and mitophagy, respond to dysfunction, with PINK1-Parkin mediating mitophagy. These pathways are important for disease and aging. Mitochondrial organization and function are complex, with structural and functional domains essential for cellular needs. Advances in research are improving understanding of mitochondrial biology and its role in disease.