Ideas are on the move. In fact, they always have been: google that phrase, and it gets just over a million hits. Even the most abstract intellectual history assumes that knowledge is not just a property of individual minds, but something that moves and is shared. Otherwise it would be impossible to undertake such basic tasks as connecting different historical periods or making statements about geographically dispersed beliefs. The aim of bringing movement to the centre of historical attention in recent years is not to repeat the banal truism that knowledge moves. What matters is understanding that movement is fundamental to the making of knowledge. The great virtue of this special issue is demonstrating how effective a consistent stress on movement can be. The essays deal with a wide range of topics in the human sciences from the mid-eighteenth through the mid-nineteenth centuries, and an equally diverse variety of geographical settings. They range from accounts of ethnographic artefacts and images to depictions in newspaper advertising of fugitives from enslavement. The essays explore long-term histories of debates about race and human unity, and how these were embedded in colonial policy and discussions of the staged development of civilisation. They involve naval officers searching for the Northwest Passage, Africans transported to the West Indies, and philosophical writers contemplating mobility as the fundamental principle for constructing a universal history.