Designers engage with sustainability in their professional practices in a variety of ways. They resort to Design for Sustainability (DfS) approaches, even though they tend to rely on intuition rather than theoretical works. They possess the ability to lead users to individual behaviour change through interventions. They have certain methods and capabilities to transform sustainability challenges into actionable and potentially sustainable futures, and certain shortcomings in skills and education as well as the challenges they face such as workplace conditions and policies which results in them prioritising other factors over sustainability. Given that, there exists a gap in the literature where the point of view on sustainability of professional designers is not adequately taken into account. Through a series of interviews based on a conceptual framework, this thesis aims to qualitatively study and understand the subjective perspective of professional designers on how they conceptualise and assess sustainability in order to detect opportunities to develop new and improved tools, methods, and approaches. Based on the interviews, designers are found to be not the decision makers around sustainability issues and they need to speak the business language to contribute to decision making. They could furthermore advocate by asking the right questions to the right people at the right time. Having said that, it is important to highlight that not everyone is passionate for sustainability and designers may be alone in their battle. Their challenge is to design solutions where user-centricity comes first and are still profitable for them to be effective. One skill of designers is that they could bring awareness via tangible ways, which is especially important for an issue as abstract as sustainability. Implications for designers is that they could look at examples for inspiration, but need to go beyond and nudging the customer is not enough, the product needs to have inherent sustainable qualities. Ultimately, sustainability is a complex, systemic issue yet design interventions are not yet holistic or integral. Through a co-creation session, the problem statement was defined based on the findings from the literature review and interviews. Stemming from a deeper need for guidance and direction, designers need inspiration to imagine new paths of navigating sustainability issues. They face challenges with advocacy for sustainability and the fight against green- washing in their organisations. They need ways of justifying their actions to managers by proving their actions with credible references and need to align and empower stakeholders with different backgrounds on sustainability issues by engaging them through compelling and accessible ways and effectively communicating with them through a common language. In response to this statement, the design intervention Tactical Sustainability Cards was developed. This tool helps the designer at hand by giving them tactics when trying to balance innovation and sustainability in the design process. They furthermore show examples from the industry to benchmark and get inspired. Additionally, they provide relevant academic sources for designers to strengthen their design work. These cards were validated through interview participant feedback and a validation session, and a final iteration is presented.