This paper outlines a theoretical approach to the study of action in simple, routine activities, along with a coding system for describing and analysing performance. The approach is exemplified through a single case study involving a patient who developed a profound action disorder following rupture of a pericallosal artery aneurysm and concomitant anterior cerebral artery spasm. The Action Coding System provides a detailed, quantitative picture of this patient's action disorder as it was manifested in two routine tasks and as it recovered over time. Discussion focuses on the cognitive organisation and processing of simple, everyday tasks and suggests how disruption of performance may ensue when intentional control of action is compromised.