Chapter 3 broaches anxieties about biological reductionism that often motivate a cautionary orientation toward biology or lurk beneath a reluctance to draw on aspects of the biological sciences for thinking about cultural and political phenomena. The chapter refigures the nature of biological matter and biological agency by tracing the composition and activity of the proteins that facilitate and regulate the cross-membrane traffic of biochemicals. The chapter explains the enabling and limiting conditions that make possible the construction of proteins by reference to genes. It proposes that these conditions allow us to account for the precision and directedness of biological activity without that activity being reducible to any one factor. It also proposes that recognition of these enabling and limiting conditions makes it impossible to identify any part of the body that is “purely” biological: the entirety of a living creature is biocultural.