The proton-linked monocarboxylate transporter (MCT) family plays a crucial role in cellular metabolism and metabolic communication between tissues. Nine MCT-related sequences have been identified in mammals, six in *Caenorhabditis elegans*, and four in *Saccharomyces cerevisiae*. MCT1 and MCT2 have been extensively studied, with detailed analyses of substrate and inhibitor kinetics following heterologous expression in *Xenopus* oocytes. MCT1 is widely expressed, particularly in heart and red muscle, where it is up-regulated during increased work, suggesting a role in lactic acid oxidation. MCT4 is prominent in white muscle and cells with high glycolytic rates, such as tumor cells and white blood cells, indicating its importance in lactic acid efflux. MCT2 has a higher affinity for substrates than MCT1 and MCT4 and is found in cells requiring rapid uptake at low substrate concentrations, including proximal kidney tubules, neurons, and sperm tails. MCT3 is uniquely expressed in the retinal pigment epithelium. The regulation of MCT expression involves alternative splicing and the use of alternative promoters. MCT1 and MCT4 interact with OX-47 (CD147), which may assist MCT expression at the cell surface. Further research is needed to characterize the properties and regulation of different MCT isoforms, which may have significant implications for health and disease.The proton-linked monocarboxylate transporter (MCT) family plays a crucial role in cellular metabolism and metabolic communication between tissues. Nine MCT-related sequences have been identified in mammals, six in *Caenorhabditis elegans*, and four in *Saccharomyces cerevisiae*. MCT1 and MCT2 have been extensively studied, with detailed analyses of substrate and inhibitor kinetics following heterologous expression in *Xenopus* oocytes. MCT1 is widely expressed, particularly in heart and red muscle, where it is up-regulated during increased work, suggesting a role in lactic acid oxidation. MCT4 is prominent in white muscle and cells with high glycolytic rates, such as tumor cells and white blood cells, indicating its importance in lactic acid efflux. MCT2 has a higher affinity for substrates than MCT1 and MCT4 and is found in cells requiring rapid uptake at low substrate concentrations, including proximal kidney tubules, neurons, and sperm tails. MCT3 is uniquely expressed in the retinal pigment epithelium. The regulation of MCT expression involves alternative splicing and the use of alternative promoters. MCT1 and MCT4 interact with OX-47 (CD147), which may assist MCT expression at the cell surface. Further research is needed to characterize the properties and regulation of different MCT isoforms, which may have significant implications for health and disease.