Drawing primarily on the Market Studies literature on Concerned-markets and Market-agencing, with reference to some Organization and New Social Movement studies on contentious markets, this thesis presents an original contribution unpacking market-agencies in controversial settings. It explores how agency is acquired and distributed across opposing socio-technical-agencements, and how these acting networks are stabilised and extended in terms of representational scope and power within a concerned-market configuration. Empirically, the study focuses on the specific case of Rothamsted GM-wheat open-air trials reviving the controversy around GM farming aimed for human consumption and food prospects between 2012 and 2017. The study relies exclusively on documentary data, mainly press data, and espouses a qualitative approach using an original method, the Cartography of Controversies, a pragmatic methodological framework specifically designed to offer a guided and progressive investigation of socio-technical debates over five observational lenses. This research favours a relational approach, examining the interconnectedness between expressed concerns and formed supporting networks, and their underpinning references and projected futures states of the world. It contributes to our understanding of market agencing by highlighting the dynamic nature of these relational arenas and by elucidating the mechanisms invested by actors in terms of representation and anchoring literatures allowing them to acquire agency and to favour their respective perspectives. Moreover, the study offers an in-depth exploration of actors’ shades of involvement, uncovering shared attributes and behavioural trends accounting for different levels and modes of agencing. Understanding both, shades of agency and counter-agencing, appears crucial to comprehend the dynamics of socio-technical agencements. The study highlights uneven distribution of agency across socio-technical- agencements, but also the central role fulfilled by counter-agencing activities aiming at stabilising acting networks and preventing their irreversibility. It underscores as well the acquired nature of matters of concern’s performativity, through a ’concerned- concerning’ process endowing them with a rallying potential enlarging their scope of influence. Special attention is given to key roles played by ’Strong Supportive Networks’ (SSN), developing a ’Perspective Speaking Potential’ (PSP), and to strategies rallying ’Potentially-concerned’ actors and impacts. From a practical standpoint, the study highlights serious divergences between clashing perspectives, especially in terms of temporality, and underpinning authorative systems and ideologies. The examined opposing perspectives seem supporting incompatible market versions, based on clashing projected states of the world and inconclusive co-existence plans, complicated further by a regulatory deadlock on some crucial questions, such as, risks of irreversible contamination and liability.