From January 2004 to July 2008, we surveyed and collected birds at 15 sites in Sabah, Malaysian Borneo. This work was designed to (1) document bird occurrence in areas and habitats that had been poorly surveyed in the past, (2) provide specimens for molecular genetic studies of bird evolution in Borneo, and (3) examine the occurrence of forest birds in agricultural and industrial tree plantations. The research disclosed new elevational, habitat, and breeding records for numerous species. It also provided insight into the biogeography of lowland endemic species in Sabah and montane endemic species in Borneo. The hypotheses formulated from these biogeographic discoveries should serve as useful frameworks for future phylogeographic work on Bornean birds.