Drawing on ethnographic research undertaken at sea in north-west Scotland, this thesis builds a labour and class analysis of human-environment and human-machine relations. Fishing 'grounds' are constituted through metabolisms of labour as fishermen develop the affordances of their environments to make them productive. Places are constituted as fishermen transform them through their labour, judge them as significant through their productivity, and name them through the social process of collectively developing their affordances. Fishermen have developed complex techniques for extending their bodily senses far beneath the sea and working there. Tension is manipulated in these extended working practices, and control over these processes must be maintained in order for them to be carried out safely. However, social relations can affect the exercise of control and the practice of maintenance to shape tools and machines around one's body and according to one's intentions. Techniques for moving through the land and seascape include tools and electronic devices such as the GPS, and market and class relations affect what tools are developed and how skippers and crew relate to them. Market pressures are incorporated into the daily lives and subjectivities of commercial fishermen, and can determine the species that are targeted and what techniques are used. They have also affected the relation between fishing boat owners, skippers, and crew as a transition from shared ownership and shared payment to casual labour and low-waged migrant labour has taken place. Class relations affect fishing techniques, subjectivities, their exposure to violence and danger in their work, their control over their own practices and skills, the balance between their work and the rest of their lives, the cosmopolitainisation of their workplaces, and their ability to develop affordances according to their own interests. Work under capitalism is regularly experienced both as an alienating and as a relational, and people develop multiple subjectivities which they draw on as they decide how to act. An 'ideology of nature' has developed with capitalist class relations and division of labour which contributes to mainstream conceptions of the sea as a wilderness where human labour is only destructive.