Volatile organic compounds (VOCs) can be a health concern in indoor air. Most Australians spend more than 90% of their time indoors where concentrations of many VOCs are usually higher than outdoors. This study characterised indoor VOCs and investigated the effects of the dwelling characteristics, building materials, occupant activities and environmental conditions on indoor VOC concentrations in 40 dwellings located in Melbourne, Australia in 2008 and 2009. A total of 97 VOCs were identified. Nine VOCs, n-butane, 2-methyl-butane, toluene, formaldehyde, acetalde-hyde, d-limonene, ethanol, 2-propanol and acetic acid, accounted for 68% of the sum of all VOCs. The median in-door concentrations of all VOCs were greater than those measured outdoors. The occupant density was positively associated with indoor VOC concentrations via occupant activities, including respiration and combustion. Terpenes were associated with the use of household cleaning and laundry products. A petroleum-like indoor VOC signature of alkanes and aromatics was associated with the proximity of major roads. The indoor VOC concentrations were nega-tively correlated with ventilation. Levels of VOCs in these Australian dwellings were lower than those from previous studies in North America and Europe. This study provides baseline information of indoor concentrations of VOCs in typical dwellings within the temperate climate zone in Australia, vital for future evaluation of indoor air quality. As demand for energy efficiency is increasing, it is likely to lead to increased dwelling air tightness and lower ventilation rates, and therefore, levels of indoor VOC can be expected to rise.