This paper uses as a starting point numerous attempts to define essay in Serbian and foreign language dictionaries of literary terms, as well as in the texts of certain authors who made a generous contribution to studying this form. Thus, essay has been characterised as 'a special artistic category' (Lukács), 'a critical form parexcellence' (Adorno), 'a system beyond genre' (Epstein). South Slavic authors have also contributed to attempts to define essay - for the first circle of authors essay is the form between three areas, 'literature, journalism and science' (Puhalo), for the second one it is 'a hybrid genre' and 'a special literary category' (Aćin, Marić), for the third circle it is 'a new representative kind of our age' (Solar), for the fourth it is literature in the most general sense and 'a style before everything' (Tomašević), for the fifth it is 'a walking form' (Pantić), for the sixth it is both a form and 'an act of thinking' (Radojičić), for the seventh 'it is one kind of genre 'yeast' in the most diverse and unexpected combinations'' (Delić) etc. In order to establish why essay is so difficult to define and in order to understand its vitalistic nature, a retrospect of its diachronic development must be made. Considering the fact that essay has permeated all aspects of contemporary literature and culture, this paper has been conceived as a necessary diachronic insight for its further theoretical study - substantial and relational, with a special amount of attention being directed at the emergence and development of essay as well as its study up to the present time and prospective study in the future in the Serbian literature.