The silicon nanowires (SiNWs) comprise a core-shell structure. Contrasted to conventional volume doping to modulate the transport properties of SiNWs, recent studies have revealed an economic and non-destructive approach to induce doping through surface engineering. In this review, extensive first principles theoretical investigations are presented which revealed the influence of surface passivation and ambience in modulating the conductivity of SiNWs. The theoretical findings rationalize several experimental results and provide useful pointers for tuning the electrical properties of nanomaterials.