It is known that motivating people to learn mathematics can be difficult. My research explores adults’ motivation to learn mathematics and focuses on learners who are overcoming many barriers to study in the workplace, in classes organised and funded by their trade union. The adults are aiming to gain a formal qualification, using less formal learning approaches, in a non-traditional context, hence this research offers teachers in more conventional education settings an opportunity to learn about successful alternative practice. Using a grounded theory approach on qualitative data and by exploring the findings within a range of sources of research literature into motivation and mathematics learning for adults, the research distinguishes between initial motivation to re-engage with learning and motivation to continue learning. It identifies the dynamic interplay in motivation between the personal needs or goals of individual learners, and the influence of other members of faceto- face learning groups. This interplay is seen as shaped in the wider context of UK society, and, in particular, by the role of trade unions. Adults in trade union organised classes report being able to successfully develop their mathematical skills and confidence through the use of ‘collective’ learning approaches, which develop positive social and emotional encounters in the classroom that are different from their previous experiences. Developing confidence while learning mathematics helps to shape their identities and, for this sample, has considerable influence on their motivations both inside and outside the classroom. The significance of developing confidence is reinforced by the adults’ use of emotional language when reporting changes in their feelings towards mathematics from negative to positive and their motivation to learn, described as an adult’s ‘Affective Mathematical Journey’. This emphasises the importance of considering the emotional connection to motivation and cognitive development when reflecting on professional practice associated with adults learning mathematics.