This dissertation presents a continuum treatment of growth in biological tissue developed within the context of modern mixture theory. The crux of this work is a careful examination of the assumptions underlying continuum thermodynamics under the condition that multiple interacting species occupy a region of Euclidean space simultaneously. The formal axiomatic treatment presented derives from these assumptions, and provides insight into the sequence of interactions among tissue mechanics, mass transport and biochemical reactions. A computational formulation built upon the theory is used to solve a broad class of numerical examples demonstrating several biophysical aspects of tissue growth.