Publisher Summary This chapter discusses the advances made in the acoustic, archival, and satellite tagging of tunas. The ultrasonic frequencies are generated by driving an annular ceramic transducer at its resonant frequency and the frequency of the signal transmitted is determined by the transducer diameter. The development of multidirectional hydrophone arrays coupled with independent acoustic receivers and computers has improved the estimation of the direction and range of fish relative to the tracking vessel used. All tracking data suggest that yellowfin, in coastal and open ocean habitats, are primarily the inhabitants of the mixed layer. In many cases, the objective of tracking has been to understand the behavior of yellowfin around fish aggregating devices and topographic features. The fish have shown very close associations with FADS and other topographic features, such as sea mounts and continental shelf edges, and there has been clear diurnal variation in their position relative to these features and their depth preferences. Direct observation of the internal muscle temperatures of the Pacific bluefin tuna revealed a relatively constant muscle temperature, ranging from 23–26°C.