Drawing on posthumanist theories from geography, anthropology, and science and technology studies (STS), this article argues that agency is shared unevenly between humans and nonhumans. It proposes that conceptualizing animals as agents allows them to enter history as active beings rather than static objects. Agency has become a key concept within history, especially since the rise of the “new” social history. But many historians treat agency as a uniquely human attribute, arguing that animals lack the cognitive abilities, self-awareness, and intentionality to be agents. This article argues that human levels of intentionality are not a precondition of agency. Furthermore, it draws on research into canine psychology to propose that dogs display some degree of intentionality and self-directed action. The aim is not to turn dogs, or any other animals, into human-style agents nor to suggest that they display the same levels of skill, intentionality, and intelligence as humans. Instead, the objective is to show how dogs are purposeful and capable agents in their own way and to explore how they interact with human agents. The article particularly considers the agency of militarized dogs, especially those on the Western Front (1914–1918), to suggest how historians can use primary sources to uncover how individuals in the past have treated dogs as capable creatures and to capture some sense of dogs’embodied and purposeful agency.