Confined by the intricate configuration of the Philippine Archipelago, forced by the monsoonal climate and tides, responding to the remote forcing from the open Pacific and adjacent seas of Southeast Asia, the internal Philippine seas present a challenging environment to both observe and model. The Philippine Experiment (PhilEx) observations reported here provide a view of the regional oceanography for specific periods. Interaction with the western Pacific occurs by way of the shallow San Bernardino and Surigao straits. More significant interaction occurs via Mindoro and Panay straits with the South China Sea, which is connected to the open Pacific through Luzon Strait. The Mindoro/Panay throughflow reaches into the Sulu Sea and adjacent Bohol and Sibuyan seas via the Verde Island Passage and the straits of Tablas and Dipolog. The deep, isolated basins are ventilated by flow over confining topographic sills, causing upward displacement of older residence water, made more buoyant by vertical mixing, which is then exported to surrounding seas to close the overturning circulation circuit.