Abstract. The R Coronae Borealis (RCB) stars are a group of H-deficient stars. The visual magnitude of these stars declines to several magnitudes at unpredictable times. The decline in their magnitude is caused by the formation of dust in the line of sight. The process that is responsible for the origin of these stars, which transforms a normal star into a H-poor RCB star, is still not clear. There are two proposed scenarios for their origin. One is the merger scenario, that involves merging of a He white dwarf with a C-O white dwarf, and the other is, the final He-shell flash that occurs at the late stages of a single star's evolution. The aim is to investigate the origin of these stars in the light of their observed spectroscopic signatures. One of the important features are the presence of 12C13C molecular bands in the spectra of these stars. The presence of 13C in their spectra is a clue to their origin. 13C is not expected in the merger scenario as most of the carbon content in the merged product has come from the C-O white dwarf, that is the triple alpha processed material 12C. Here, I will present the observed spectroscopic clues that can explain the origin of these stars.