In this talk we will present and discuss the perspective, prospects, and problems of gradient structures, especially in the nano-scale. Gradient structures are formed and evolved naturally in many biological systems such as bones and plant stems for superior mechanical and functional properties. They have been engineered into mechanical parts via thermochemical routes such as nitriding and surface heat treatments. Recently gradient structures with grain size gradient from nano-scale to micro-scale were introduced into metals, producing excellent strength and ductility. Materials with gradient structures represent an emerging academic field with many fundamental and engineering problems to be solved by researchers from the communities of materials science and materials mechanics. Some of the issues can only be solved by team effort from both experimentalists and theorists.