Recently Berkovits and Vafa have shown that the bosonic string can be viewed as the fermionic string propagating in a particular background. Such a background is described by a somewhat unusual N = 1 superconformal system. By coupling it to N = 1 supergravity I construct a local supersymmetric action for the bosonic string. † e-mail: fiorenzo@nbivax.nbi.dkIn a recent paper Berkovits and Vafa [1] have shown how to embed the bosonic string into the N = 1 superstring. After identifying a suitable N = 1 superconformal system which could be used as a background for the N = 1 string, they showed how the bosonic string amplitudes are reproduced by the fermionic string propagating on it. They also showed how to view the N = 1 string as the N = 2 string moving in a particular background, and were led to conjecture the existence of an "universal string theory" which contains all string theories as particular choices of the vacuum (see also ref.[2] for some interesting remarks on the search for an universal string theory). In this letter I analyze the structure of the N = 1 superconformal system used by Berkovits and Vafa to embed the bosonic string into the N = 1 string. I look at the classical limit of such a system and by coupling it to N = 1 supergravity I shall produce a locally supersymmetric action for the bosonic string. I will conclude presenting few comments on its quantization and on its relation to the usual bosonic string action.I start by recalling the Berkovits-Vafa superconformal system. It is realized on a matter system with stress tensor T m and central charge c = 26 plus an anticommuting bc-system (b 1 , c 1 ) of spin ( 3 2 , − 1 2 ). The generator of the N = 1 superconformal algebra areand their OPE generates a superconformal algebra with c = 15. For simplicity I will consider the matter system as given by the usual 26 free scalar fields X i , and omit showing the index i in the following. By dropping the improvement terms in (1), i.e. considering the generatorsand keeping only single contractions in their OPE, one obtains a classical superconformal algebra without central charges. Such a superconformal algebra, together with its rightmoving counterpart, describes the classical symmetries of the action1The supersymmetry transformation rules can be easily computed from the generators and read δX = ǫc 1 ∂X +ǭc 1∂ X,where∂ǫ = 0 and ∂ǭ = 0. This realization of supersymmetry is quite unusual. It looks spontaneously broken (δc 1 = ǫ + . . .) and it is non-linearly realized. For this last reason it is difficult to rewrite the model with superfields and couple it to supergravity using standard superspace techniques. However, one can follow another well-known path, that of using the Noether method to gauge global symmetries. This was in fact the strategy used in [3] to construct a locally supersymmetric action for the spinning string. I will now follow the same path for the Berkovits-Vafa supersymmetric model and obtain a locally supersymmetric action for the bosonic string. The coupling to gravity is straightf...