This article uses perspectives from science and technology studies to understand the working knowledge used by operators to understand and handle machines. Industrial production is seen as a heterogeneous assemblage of sociomaterial practices, where machines and humans interact in processes of mutual inscription and modification. Working knowledge is analysed as situated practices of knowing, or performances.This perspective is used in a meta-interpretation of earlier ethnographic research and other accounts of manual, industrial work, focusing on the mental, bodily and emotional understanding employed in crucial situations, as when learning to work, localizing machines, or coping with difficult or recalcitrant machines. Copyright © 2008 BSA Publications Ltd.