Tree growth is limited by either carbon availability (carbon limitation) or the ability to use available carbon (sink limitation); when and where each mechanism prevails remains unclear despite the importance to population/community dynamics and ecosystem functioning. Recently, debate over carbon versus sink limitation to tree growth has increased in many specific cases: the causes of reduced growth and survival during drought, the lack of tree growth above alpine treelines, and reduced growth with tree height or forest stand age. The purpose of this session is to draw all these separate debates together to consider the general case for carbon or sink limitation. We hope that by doing so, these similar cases can add valuable insight to each other, as well as help us to build a more comprehensive understanding of carbon and sink limitation. The first half of the session will be devoted to talks about sink versus carbon limitation under specific conditions and in particular ecosystems. Confirmed speakers will present original work addressing whether trees are carbon or sink limited (or both) under water stress, at alpine treelines, in mature forest stands, and under future CO₂ levels. The second half of the session will address carbon and sink limitation more generally with discussions of how carbon and sink limitation can (or cannot) be distinguished from each other, why they occur, and the implications of these two types of growth limitations to other areas of study (such as ecosystem carbon cycling). Confirmed speakers will address how the stored carbohydrate pool in trees (commonly used as evidence for or against carbon limitation) relates to growth and growth limitation, and whether it can be used as a reliable indicator of limitation. Finally, speakers will discuss how incorporating both sink and source mechanisms for growth limitation into ecosystem flux models can improve model performance and predictions.