"Although behaviours associated with territory maintenance are extensively studied, little is known about the establishment of territorial boundaries, a key process influencing individual fitness and population demography. In this regard, conspicuous features of the landscape and constructions such as scent marks (landmarks) can have an effect on whether and where boundaries are established. Landmarked boundaries have also been associated with altered social interactions, particularly contests that take place on boundaries. Some of these landmarks physically constrain a resident's perception or movement and may thus make the use of space beyond the landmark too costly. Other landmarks are purely conspicuous and appear to have no constraining effect, yet still have strong influences on boundary location by affecting social interactions. Factors that may influence whether a landmark is adopted for a boundary include the properties of the resident, properties of the landmark and the rate of encounter between neighbours. The purpose of this review is to consolidate and explicitly describe hypotheses relating to landmarked boundaries and highlight areas most in need of research. Ultimately, understanding the decision to adopt landmarked boundaries and the implications of these decisions for territorial populations is critical for understanding the link between landscapes, individual decisions and population ecology. (C) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved."