A detailed gravity study of Tenerife constrains the internal structure of the island and its active magma system. The maximum Bouguer anomaly (2636 gu, 1 gu=10-6 m s-2=0.1 mGal) occurs over the SW part of the postshield Las Ca¿adas edifice (LCE), while smaller highs occur over the eroded shield volcanoes. The main high extends NE and NW over the adjacent Dorsal and Santiago rift zones. A deep low occurs over the northern LCE and Teide volcano. The power spectrum of the anomalies suggests shallow causative structures (<~3 km), inferred to belong to the island's dense core. A model computed from the anomalies uses core and carapace densities of 2900 and 2360 kg m-3, respectively, except beneath the main high, where the core requires a higher density (3210 kg m-3). This part of the body is interpreted as a buried mafic volcano of substantial size, the Boca Tauce volcano, containing an old mafic plutonic complex. The enigmatic Las Ca¿adas caldera that truncates the LCE shows strong asymmetry. Dense materials occupy the southern part whereas low-density materials occupy the northern part to 2--3 km depth, consistent with a vertical collapse origin. High-density materials in the south are related to the interacaldera extension of the Dorsal rift zone. The boundary between subcaldera domains is interpreted as the buried head of the giant Icod landslide valley. The Icod landslide appears to have modified the caldera, truncating its northern side, and to have subsequently controlled the location of the active Pico Teide-Pico Viejo vent systems. Voluminous chaotic deposits lying off northern Tenerife, previously associated with the formation of the caldera and Icod valley, are better interpreted as being derived from older mass wasting events. The southern LCE has been buttressed against lateral failure by the buried Boca Tauce volcano. ¿ 2000 American Geophysical Union