This paper explores the connection between perturbative gauge theory and string theory in twistor space. Edward Witten argues that the perturbative expansion of N=4 super Yang-Mills theory is equivalent to the D-instanton expansion of a topological B model with target space CP^{3|4}. The key idea is that the tree-level scattering amplitudes in Yang-Mills theory, particularly the maximally helicity violating (MHV) amplitudes, are holomorphic functions in twistor space and are supported on certain holomorphic curves. This is interpreted as a consequence of the equivalence between the perturbative expansion of N=4 super Yang-Mills and the D-instanton expansion of the topological B model. The paper begins by discussing the properties of Yang-Mills helicity amplitudes, particularly the MHV amplitudes, which are holomorphic functions of spinor variables. These amplitudes are derived from the scattering of massless particles and are described using spinors and twistor space. The paper then describes the Fourier transform of these amplitudes from momentum space to twistor space, showing that they are supported on holomorphic curves. This is interpreted as a result of the equivalence between the perturbative expansion of N=4 super Yang-Mills and the D-instanton expansion of the topological B model. The paper also discusses the implications of this equivalence, including the possibility that the closed string sector of the B model could describe N=4 conformal supergravity. However, the paper notes that many aspects of the B model remain unclear, particularly the closed string sector. The paper concludes by highlighting the importance of understanding the relationship between gauge theory and string theory in twistor space, and the potential for using this framework to describe a wide range of physical phenomena.This paper explores the connection between perturbative gauge theory and string theory in twistor space. Edward Witten argues that the perturbative expansion of N=4 super Yang-Mills theory is equivalent to the D-instanton expansion of a topological B model with target space CP^{3|4}. The key idea is that the tree-level scattering amplitudes in Yang-Mills theory, particularly the maximally helicity violating (MHV) amplitudes, are holomorphic functions in twistor space and are supported on certain holomorphic curves. This is interpreted as a consequence of the equivalence between the perturbative expansion of N=4 super Yang-Mills and the D-instanton expansion of the topological B model. The paper begins by discussing the properties of Yang-Mills helicity amplitudes, particularly the MHV amplitudes, which are holomorphic functions of spinor variables. These amplitudes are derived from the scattering of massless particles and are described using spinors and twistor space. The paper then describes the Fourier transform of these amplitudes from momentum space to twistor space, showing that they are supported on holomorphic curves. This is interpreted as a result of the equivalence between the perturbative expansion of N=4 super Yang-Mills and the D-instanton expansion of the topological B model. The paper also discusses the implications of this equivalence, including the possibility that the closed string sector of the B model could describe N=4 conformal supergravity. However, the paper notes that many aspects of the B model remain unclear, particularly the closed string sector. The paper concludes by highlighting the importance of understanding the relationship between gauge theory and string theory in twistor space, and the potential for using this framework to describe a wide range of physical phenomena.