Cytokinins are mobile phytohormones that regulate plant growth, development, and environmental adaptability. The major cytokinin species include isopentenyl adenine (iP), trans-zeatin (tZ), cis-zeatin (cZ), and dihydrozeatin (DZ). The spatial distributions of different cytokinin species in various organelles, cells, tissues, and organs are primarily shaped by biosynthesis via isopentenyltransferases (IPT), cytochrome P450 monooxygenase, and 5'-ribonucleotide phosphohydrolase, as well as by conjugation or catabolism via glycosyltransferase or cytokinin oxidase/dehydrogenase. Cytokinins bind to histidine receptor kinases in the endoplasmic reticulum or plasma membrane and relay signals to response regulators in the nucleus via shuttle proteins known as histidine phosphotransfer proteins. The movement of cytokinins from sites of biosynthesis to sites of signal perception usually requires long-distance, intercellular, and intracellular transport. In the past decade, ATP-binding cassette (ABC) transporters, purine permeases (PUP), AZA-GUANINE RESISTANT (AZG) transporters, equilibrative nucleoside transporters (ENT), and Sugars Will Eventually Be Exported transporters (SWEET) have been characterized as involved in cytokinin transport processes. This review begins by introducing the spatial distributions of various cytokinins and the subcellular localizations of the proteins involved in their metabolism and signaling. Highlights focus on an inventory of the characterized transporters involved in cytokinin compartmentalization, including long-distance, intercellular, and intracellular transport, and the regulation of the spatial distributions of cytokinins by environmental cues. Future directions for cytokinin research are also discussed. Key words: cytokinin, biosynthesis, transporter, signal transduction, environmental changes Cytokinin metabolic pathways have been well characterized. The key enzymes involved in cytokinin metabolism are as follows: isopentenyltransferase (IPT) catalyzes the transfer of isopentenyl groups to the adenine of ATP and ADP, thereby producing isopentenyladenine nucleotides; cytochrome P450 (CYP) monooxygenase enables hydroxylation of iP nucleotides to produce zeatinnucleotides; and cytokinin riboside 5'-monophosphate phosphoribohydrolase encoded by the LONELY GUY (LOG) gene converts inactive cytokinin nucleotides to active free base forms in one step. After cytokinin biosynthesis, O- and N-glucosyltransferases are responsible for cytokinin glucosylation, and cytokinin oxidase/dehydrogenases (CKCytokinins are mobile phytohormones that regulate plant growth, development, and environmental adaptability. The major cytokinin species include isopentenyl adenine (iP), trans-zeatin (tZ), cis-zeatin (cZ), and dihydrozeatin (DZ). The spatial distributions of different cytokinin species in various organelles, cells, tissues, and organs are primarily shaped by biosynthesis via isopentenyltransferases (IPT), cytochrome P450 monooxygenase, and 5'-ribonucleotide phosphohydrolase, as well as by conjugation or catabolism via glycosyltransferase or cytokinin oxidase/dehydrogenase. Cytokinins bind to histidine receptor kinases in the endoplasmic reticulum or plasma membrane and relay signals to response regulators in the nucleus via shuttle proteins known as histidine phosphotransfer proteins. The movement of cytokinins from sites of biosynthesis to sites of signal perception usually requires long-distance, intercellular, and intracellular transport. In the past decade, ATP-binding cassette (ABC) transporters, purine permeases (PUP), AZA-GUANINE RESISTANT (AZG) transporters, equilibrative nucleoside transporters (ENT), and Sugars Will Eventually Be Exported transporters (SWEET) have been characterized as involved in cytokinin transport processes. This review begins by introducing the spatial distributions of various cytokinins and the subcellular localizations of the proteins involved in their metabolism and signaling. Highlights focus on an inventory of the characterized transporters involved in cytokinin compartmentalization, including long-distance, intercellular, and intracellular transport, and the regulation of the spatial distributions of cytokinins by environmental cues. Future directions for cytokinin research are also discussed. Key words: cytokinin, biosynthesis, transporter, signal transduction, environmental changes Cytokinin metabolic pathways have been well characterized. The key enzymes involved in cytokinin metabolism are as follows: isopentenyltransferase (IPT) catalyzes the transfer of isopentenyl groups to the adenine of ATP and ADP, thereby producing isopentenyladenine nucleotides; cytochrome P450 (CYP) monooxygenase enables hydroxylation of iP nucleotides to produce zeatinnucleotides; and cytokinin riboside 5'-monophosphate phosphoribohydrolase encoded by the LONELY GUY (LOG) gene converts inactive cytokinin nucleotides to active free base forms in one step. After cytokinin biosynthesis, O- and N-glucosyltransferases are responsible for cytokinin glucosylation, and cytokinin oxidase/dehydrogenases (CK