In this introductory paper, we review observations and theories of the low-latitude western boundary currents in the Pacific Ocean and the Pacific-to-Indian Ocean throughflow, including the new results presented in this special section. In addition, we summarize issues and questions that remain to be addressed. In particular, we point to the need for completing the zero-order description of the mean and seasonal variation of the circulations of the region. ¿ American Geophysical Union 1996