This paper conceptualises a basis for understanding learning in workplaces. This comprises a duality between how access to workplace activities and guidance is afforded, on the one hand, and how workers elect to engage with what is afforded to them, on the other. This reciprocal basis for thinking, acting and learning is referred to as co-participation at work. The key contributions that workplaces make to workers' learning comprise learners' access to workplace activities and guidance. Yet workplaces are contested environments, where participation and learning are shaped by the affordances extended to workers or cohorts of workers that are subject to workplace norms and practices. Consequently, access to these contributions is not equally afforded. How they are distributed and accessed shapes how the workplace invites individuals to participate in and learn from these experiences. Yet, individuals also actively participate in managing their learning. They construe the invitational qualities of what is afforded them and elect to engage with work activities and also shape what they learn. Engagement in work and what is co-constructed through work is negotiated between the evolving social practice of the workplace and individuals' ongoing development founded in their ontogeneses. (Contains 2 figures.)