Eco-designed products can contribute to sustainable development if consumers choose them rather than the less environmentally friendly alternatives and if they are used properly. However, eco-design methods have so far failed to address the issue of unsustainable behaviors, whose sources have not been recognized. In light of this deficiency, the authors have analyzed a large number of eco-designed products with the aim to capture the possible unsustainable behaviors arising from their use and consumption. The subsequent characterization of unsustainable behaviors has led to the creation of a framework of unsustainable behaviors, which has been subjected to the evaluation of a pool of experts in the field. In its final version, the framework includes nine classes of unsustainable behaviors, which are categorized into the corresponding product lifecycle phases (purchase, use, end of life), and different kinds of undesired effects (harmful, insufficient, excessive) based on the TRIZ-oriented functional analysis. The classes, whose significance has been checked in the literature, include frequent causes of unsustainable behaviors and corresponding examples. Through the framework, designers can take into due account the possible circumstances that would prevent their developed products from being prone to unsustainable behaviors. In a future step, the classes of unsustainable behaviors are to be linked with indications arising from Design for Sustainable Behavior.