There is a more than ever need to be critical of the present and imagine future possibilities. Several critical approaches to design place its efforts in creating artefacts for critical reflection. As part of the spectrum, speculative design is an approach that, through speculation into the possible, aims to challenge the status quo, explore the implications of emerging issues, and frame debate around matters of concern. While the goal of speculative design is in engaging publics in debate and exploring alternatives to the dominant narrative, the practise has been facing several critiques. More specifically, speculation as remained exclusive to the designer as an author and most of the work is disseminated in gallery spaces, limiting the reach and depth of the debate generated. New projects and practitioners have emerged that push speculative design work into new contexts and within a participatory mindset. This thesis is placed at this intersection between participation and speculative design. While this intersection seems promising and valuable, there might be some challenges in the transition from authorial practise to a participatory process. Additionally, bringing speculative design in new contexts might bring several risks, specially when practised within the domains it aims to critique. The main research question addressed by this thesis is the following: When we open up the speculative design process, is the practise able to retain the critical aspects related to it? Eight semi-structured interviews with leading practitioners working on this space were done. From the interviews, three main challenges were identified: “Stuck in a Singular View” refers to the challenge of engaging a plurality of voices and on maintaining a nuanced perspective when critically discussing the future; “Stuck in the Context” is related with the difficulty in engaging in self-reflexive behaviour when working with speculative design inside contexts that might be reluctant to critique; “Stuck in the Now” refers to the difficulty in working in the future and how short-sightness might create an obstacle to speculative thinking. Additionally, several issues were mapped from the interviews and brought in a provisional framework for participation in speculative design. This framework consists of four levels that represent different aspects of the process: Context of Operation, Participants, Moments of Engagement, and Outcomes. Finally, the four levels and the three main challenges were used to problematise the design space and create a critical toolkit for integrating participation in speculative design. The goal of the toolkit is not to provide a solution on how to this, but it proposes several different questions and issues for reflection. The toolkit consists of 37 issues, spread throughout the four levels and in relation to the three challenges. The issues took shape as hexagonal playing cards, making it possible to connect the different cards and explore the design space.