Organisms and their place in biology

In this paper we review the concept of organism analysing the main ideas related to it in the context of present biological theories. The discussion is focused and developed according to four key issues: individuality, organisation, autonomy and reproduction. Once these basic connections are established, a spectrum of possible entities that fall under the label ‘organism' is looked over, with special emphasis on limit or controversial cases. The aim is to see whether they all share a set of common features and, if they do, why it is so difficult to reach a consensus on the definition of the term. Finally, we try to release somehow the tension between those hierarchical schemes proposed to account for life as a global phenomenon and those approaches that take organisms as the central target of (theoretical) biology, suggesting a possible middle-ground solution open for further research.