The global ocean is composed of parts—its regions—each playing a role in the global scheme of the ocean and climate systems. Each region has its intrinsic interest and uniqueness. Of course, the same physics applies to all, but by virtue of position, topographic constraints, and coupling to the atmosphere, some regions attract more interest than others; some are more central to the larger-scale systems. The tropical seas of Indonesia are such a place. There, Pacific water flows into the Indian Ocean amid a complex array of islands and of deep and shallow seas connected by narrow passages of varied depths. Stratification is subject to intense tidal-induced mixing, all under an atmosphere regulated by the Asian-Australian monsoons and subject to the whims of the El Niño Southern Oscillation. Understanding the interplay of these variables provides a challenge that oceanographers can’t resist.