Abstract
For more than twenty years, strong Fell emission lines have been observed in active galactic nuclei and quasars. In the state of our knowledge, we are able neither to properly explain their strengths nor to fully determine the characteristics of their emitting region. In this paper is given a quick overview on the results of the spectroscopic observation of these lines, as well as a summary of the atomic data available to characterize the very complex Fell atom. The main models proposed to interpret the observations are then described and the influence of the physical parameters is outlined. The most successful model, up to date, to depict the region emitting the Fell lines, is proposed as a conclusion.
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