Abstract: 
I will present a modification of twistor string theory which
gives the spectrum of super YangMills theory coupled to Einstein
supergravity instead of the higher derivative conformal supergravity
arising in the original twistor string models of Witten and of
Berkovits. After reviewing elements of twistor theory and of the
worldsheet formulation of the Berkovits model, I will describe the
symmetries of the socalled betagamma systems and their gauging. I will
then explain how the analysis can be applied to the construction of a
family of new gauged Berkovits twistor strings which are free from
worldsheet anomalies. The new theories include one with the spectrum
of N=8 supergravity, two theories with the spectrum of N=4 supergravity
coupled to N=4 YangMills, a family of N>0 models with the spectra of
selfdual supergravity coupled to selfdual superYangMills, and a
nonsupersymmetric string with the spectrum of selfdual gravity coupled
to selfdual YangMills and a scalar. Time permitting, I will discuss
what is known about the interactions in the new theories.
