This thesis is an account of the stratigraphy and structure of Portuguese Timor (an area of. 16,000 sq. km.) supported by four geological maps (1:100,000).. Twenty four formations are distinguished, four of' which are allochthbnous. The autochthonous formations range in age from Lower Permian to Recent, and make up a section of 8000 metres thickness.Of the allochthonous formations one is pre-Permian, two are Permian, and the other a midMiocene gravity slide deposit. The lithology and petrography of each formation is described, the fauna and flora recorded, and the environment of deposition discussed.As limestones are the predominant rock type in Timor special attention has been paid to limestone petrography.Five separate periods of folding are recognised, two of which, the Timorean and the Ramelauean, were of major importance and accompanied by large scale overthrusting.