A large number of methods have been developed in order to systematically consider sustainability as a design criterion in the product development process. However, further support is required to help product development teams to assess the applicability of the existing methods in the specific design contexts. In order to address this problem, the Design Decision Support Assistant (DDSA)—an IT-based assistance system—has been developed to support product development teams in the selection, scheduling, and application of sustainable product design methods in the product development process. The backbone of the assistant is a method repository comprising 29 methods for sustainable product development as well as a method taxonomy to enable the selection and scheduling of suitable methods for achieving sustainability-related design targets. This article introduces the concept of the DDSA, details its practical prototypical implementation, and illustrates its application in a case study.