Smart grid will integrate the state-of-the-art ICT technologies to significantly improve the efficiency, sustainability, security, and stability of the traditional power grid. In this talk, we will present our recent studies to address two major challenges in the smart grid: greenness and cyber security. In particular, the talk mainly includes three parts. In the first part, we introduce the smart grid scenarios, key concepts, and communications architectures. In the second part, we will present the greenness aspect based on a game-theoretical demand response management framework. In the third part, we will present cyber security aspects and a context-aware authentication scheme in Vehicle-to-Grid (V2G) communications systems when there is wide penetration of Electronic Vehicles.