Additive Manufacturing (AM) is a type of material joining process whereby parts can be directly fabricated from its 3D model by adding materials typically in a layer by layer fashion. Compared to conventional manufacturing techniques, AM has some unique capabilities which bring significant design freedom for designers. Some of this design freedom is manifested in the innovative design of lattice structure to achieve multifunction with reduced weight and consolidated component designed with reduced part count and improved performances. A new type of design philosophy for AM is emerging that is to achieve integrated functions and part consolidation, which plays a significant role in sustainable design. This chapter discusses this new design philosophy with a thorough review of lattice structure design and optimization methods, design for AM methods, and other related new design methods. It presents a general design framework to support sustainable design for AM via functionality integration and part consolidation. This proposed general design methodology supports the design that has less part counts and less material but without compromising its functionality. A case study is given at the end of the chapter to illustrate and validate the proposed design methodology. The result of this case study shows that the environmental impact of a product’s manufacturing process can be reduced by redesigning the existing product based on the proposed design methodology. Moreover, compared to its original design, the redesigned product also has a lower part count. Generally, this case study implies that design freedom enabled by AM is an indispensable factor which needs to be considered during the environmental impact analysis of products fabricated by AM processes.