Employee or staff engagement has an elusive, hidden quality with a premium appeal. Here, engagement specifically refers to behavioural engagement; the extent to which people cooperate in groups and exhibit pro-social helping behaviours. These are effects that have been associated with the field of procedural justice, a field which is concerned with the capacity of processes to enhance a sense of fairness and in so doing encouraging cooperation, trust, and organisational citizenship behaviours. This study has demonstrated that it is possible to rapidly increase engagement levels, evidenced by participation in innovation activities, and provide a way of sustaining this in the longer term through forming new trusting relationships. A range of process management techniques, communications tools, and managerial behaviours, based on a review of established theories in the field of procedural justice, was tested, validated and refined for their ability to contribute to attitude shifts related to encouraging behavioural engagement. These were integrated into an established innovation framework and employed in an elaborate and ambitious Action Research field study involving 750 people, and over 18 months of field work. This longitudinal qualitative research differd substantially from the correlation studies that are the norm in the field. Critically, it enabled justice to be researched 'as it was happening' and to develop theory based on the complex interplay of phenomena and rich context. Using an established model of procedural justice as an explanation, it was found that the quality of treatment participants received was significantly more important than the quality of the processes used to organise activities or make decisions, when attempting to encourage cooperative behaviour associated with innovation. Unlocking engagement was found to be about unlocking identification by providing a valuable reason for people to express discretionary behaviour and by appealing to socio-emotional motivations for increased status within the group or to reciprocate fair treatment. The changes experienced in the quality of relationships in the group, described in terms of social capital, were seen to contribute to the longer term value of the implementation approach used