While Sir Jospeh Banks is best known for his role as botanist on Captain James Cook's Endeavour voyage, it was his activities in promoting commercial biology that had the greatest long-term efect on the British Empire. Banks' fame following Cook's first voyage, his friendship with King George III, and his position as President of the Royal Society provided him with significant influence within government and private British institutions. It is the contention of this thesis that Banks' influence was so profound that, as an individual, he contributed significantly to the direction and form British imperial policy took during the five decades between 1770 and 1820. Through the development and application of commercially useful species and the organization of a world-wide network of botanic gardens Banks became a key figure in British imperial expansion. This thesis is divided into three segments. The first examines Banks' early experiences with commercial biology with the aim of providing a contextual basis for his later ventures in ecological imperial expansion. The second section considers three such ventures in which Banks was involved. The three case studies (the breadfruit expeditions, the establishment of King George III's flock of merino sheep, and the attempted cultivation of hemp for naval stores within the confines of the British Empire) highlight Banks' vision of how commercial biology could enhance the British Empire and the extent to which British institutions (e.g., British government, Royal Navy, East India Company, planter class in the British Caribbean) relied on Banks' guidance and knowledge in matters of ecological imperial expansion. The third segment discusses Banks' patronage in the establishment of a series of botanic gardens. These gardens served four important imperial functions. They promoted the expansion of British territorial borders, served as centres for the discovery and development of new resources, provided a means of promoting the imperial status of Britain through the display of exotic plants, and established a network of inter-connected links for the exchange of natural resources, information, and ideals between widely separated British territories.