SummaryTidemann, S.C. (1990). Factors affecting territory establishment, size and use by three co-existing species of fairy-wrens (Malurus).Emu90, 7–14.SuperbMalurus cyaneus, VariegatedM. lambertiand White-wingedM. leucopterusFairy-wrens co-existed at Booligal, New South Wales, where their territories overlapped but very few interspecific interactions were observed. Territories were established and maintained by song and less often chases between males. During nesting, the area utilised by the fairy-wrens was smaller than that established earlier. Areas that were grazed heavily were occupied less, especially by Superb Fairy- wrens. Fairy-wrens enlarged their territories during drought. Size of a territory correlated positively generally with the number of bushes contained within it except during drought. Territory size correlated negatively with insect abundance for Superb and White-winged Fairy-wrens only and with the number of groups of each species except where vegetation was patchy. I suggest that territory quality can be described best in terms of food availability, and for gleaning insectivores this may depend on the foraging area available.