Biology differs from most sciences in its particular way of dealing with the term ‘function’. On the one hand, questions like ‘What is the function of a trait x?’ seem to be perfectly legitimate, realizing that (most) biologists acknowledge that “function is a concept that to this day remains indispensable to biology” (Keller, 2010: 19). On the other hand functional explanations, along with intentional explanations, generally have one main disadvantage in common: they are teleological or seem to invoke a ‘causa finalis’. As a consequence, they are not in line with the scientific practice of explaining causality in terms of a ‘causa efficiens’. Moreover, they are claimed to be untestable (Hempel, 1965) and suggested to lead to storytelling in evolutionary biology (Gould and Lewontin, 1979; Buller, 2005), rather than to a sound scientific approach. As a reaction, efforts were made to demystify and/or naturalize functional explanations in biology. Two opposite approaches are generally distinguished: Historical approaches include Wright’s account of functions (Wright), proper function theory (Millikan, 1989), and the etiological approach (Perlman, 2010; Buller, 1999). Examples of a-historical accounts are the systemic approach (Cummins, 1975), goal contribution approach (Nagel, 1961; Boorse, 1976), life chances approach (Canfield, 1964; Wimsatt, 1972) and dispositional view (Bigelow and Pargetter, 1987). Both historical and a-historical approaches meet a number of problems. Above all, attempts to unify (Kitcher, 1993; Walsh, 1996), purify (Cummins & Roth, 2010) and instantiate (Griffiths, 1993) have only increased the amount of theories on functional explanations, making it even more difficult to maintain a clear view on the matter and the problems surrounding it. Attempts to introduce a pluralistic account, such as Wouters (2005), have tried to identify ways in which the term function is used in connection with the study of living organisms; trying to grasp how biologists appeal to function. Although promising, his account is lacking to certain extents, such as his central focus on intuitions as a guideline for the function debate. In this paper, attempts are made to reconcile and combine the advantages of the accounts mentioned, avoiding the problems (e.g. function/malfunction distinction, promiscuity of function-objection, causal asymmetry, function-setting history) these accounts are faced with. This paper contributes to the causality/explanation debate (in biology) in at least three ways: First, in respect to the time frame of the presentation, an overview of the existing accounts and approaches to functional explanation in biology will be given, which is missing in the literature, rendering some contemporary discussions superfluous. Second, a bottom-up, pragmatic, context-sensitive and pluralistic framework capable of dealing with functional explanation in scientific practice will be presented, guided by answers to central questions, such as ‘Are we to choose between accounts?’ and ‘Are the proposed accounts incompatible and/or excluding?’. In detail, a relational theory of biological function able to combine the historical and a-historical approaches mentioned serves as underlying guideline to fully grasp examples from actual scientific practice (i.e. molecular gene biology and systems biology). This pluralistic theory defends that the function of a state or trait is not an intrinsic property, but always stands in relation to an environment. Therefore, a trait may have different functions with respect to different environments at the same time. Third, in view of the topic of the conference, special attention will be given to the teleological character of functional explanation, addressing the scientific merits and/or pitfalls of causality-debate in terms of ‘causa finalis’.