Book excerpt: In the second half of the nineteenth century a new kind of social and cultural actor came to the fore: the expert. During this period complex processes of modernization, industrialization, urbanization, and nation-building gained pace, particularly in Western Europe and North America. These processes created new forms of specialized expertise that grew in demand and became indispensible in fields like sanitation, incarceration, urban planning, and education. Often the expertise needed stemmed from problems at a local or regional level, but many transcended nation-state borders. Experts helped shape a new transnational sphere by creating communities that crossed borders and languages, sharing knowledge and resources through those new communities, and by participating in special events such as congresses and world fairs.