Employing a technological approach derived from the 'Anthropology of Technology' theoretical literature, this thesis concerns the identifi cation and explanation of change in prehistoric extractive metallurgical behaviour in the Khao Wong Prachan Valley of central Thailand. The 'Valley' metallurgical complex, amongst the largest in Eurasia, constitutes Southeast Asia's only documented industrial-scale copper-smelting evidence. The two smelting sites investigated, Non Pa Wai and Nil Kham Haeng, provide an interrupted but analytically useful sequence of metallurgical consumption and production evidence spanning c. 1450 BCE to c. 300 CE. The enormous quantity of industrial waste at these sites suggests they were probably major copper supply nodes within ancient Southeast Asian metal exchange networks. Excavated samples of mineral, technical ceramic, and slag from Non Pa Wai and Nil Kham Haeng were analysed in hand specimen, microstructurally by refl ected-light microscopy and scanning electron microscopy (SEM), and chemically by polarising energy dispersive x-ray fl uorescence spectrometry ([P]ED-XRF) and scanning electron microscopy with energy dispersive x-ray fl uorescence spectrometry (SEM-EDS). Resulting analytical data were used to generate detailed technological reconstructions of copper smelting behaviour at the two sites, which were refi ned by a programme of fi eld experimentation. Results indicate a long-term improvement in the technical profi ciency of Valley metalworkers, accompanied by an increase in the human effort of copper production. This shift in local 'metallurgical ethos' is interpreted as a response to rising regional demand for copper in late prehistory.