This report presents innovations from academia and practice designed to green grey infrastructure assets such as bridges, street furniture and coastal engineering structures that need to remain primarily grey for their essential function. We call this integrated green grey infrastructure (IGGI). We collated material on these innovations and assessed them using a critical success factors (CSF) framework that we –co-developed with a team of practitioners in government agencies and companies to help better evaluate the potential benefits and limitations of using IGGI measures compared to traditional grey engineering solutions. The CSF framework is outlined and demonstrated by assessing the engineering performance and ecosystem services benefits of ecological enhancements used in specific operational scale case studies. The case studies presented in this report show that simple, inexpensive ecological enhancement and green engineering solutions can deliver more multifunctional benefits than business as usual solutions for similar or reduced costs. These ecological enhancements and green engineering options have been compiled and assessed for historic conservation areas, urban areas, estuaries and at the coast. This report is intended to support asset managers, engineers, conservation and biodiversity teams, decision-makers, and other end-users to help them better identify IGGI options and evaluate these against business as usual grey engineering approaches.