This document investigates a set of projects I call DIY Infrastructure, in which designers are building alternative infrastructural systems. Through these projects, new actors-often non-experts-reveal and re-imagine long-established social and technological relationships which were previously off limits to them. These projects are significant to the study of design and digital media for the following reasons:First, they detail a new area of design. The designers of DIY infrastructure present an expansion of the scope of design coupled with a nuanced and almost paradoxical understanding of infrastructure as an intractable and exceedingly complex problem. At the same time, their work reveals the extensive social and political effects of existing design decisions-the far-reaching consequences of the design decisions which formed existing infrastructure. These decisions are in play across a variety of scales of time and space, affecting individual bodies as much as continental ecosystems, and shaping personal behavior as much as global commerce and trade.Second, they expand the scope of digital media studies. Digital media studies often overlook infrastructure, in spite of their interdependence. Digital media are involved in areas including the control and monitoring of the electrical system, the treatment and movement of water and sewage, and the routing of freight through intermodal shipping systems. The study of DIY infrastructure design, and infrastructure more broadly, exposes the role of digital media in shaping these overlooked aspects of modern life. There is an invisible relationship between digital media, infrastructure, and political authority, and it includes the interdependence of infrastructure and the contingent nature of our ongoing reliance on these complex sociotechnical systems.For example, Cloacina is the project of two activists developing a new municipal waste disposal system in which a decentralized networked system significantly lessens the amount of water used in processing human waste. Another project, Feral Trade Courier, employs the sort of shipping database we might associate with FedEx or UPS to facilitate an alternative shipping infrastructure, in which volunteers transport goods in an ad hoc freight network.I begin by surveying and defining DIY practice, delineating the properties of infrastructure, and determining the ways that those properties and practices can be augmented or diminished by the affordances of digital media. Next, I review the attributes that these DIY infrastructure projects share before revealing their significance through in-depth case studies. Finally, each of these case studies highlights a particular lesson from DIY infrastructure. Feral Trade Courier exposes the role of the social and the subjective in the design of logistics systems. Village Telco and Fluid Nexus show us that the relationship between established infrastructure and DIY infrastructure can be both complementary and antagonistic. Cloacina provides us an example of a way that DIY infrastructure might scale up and effect lasting sociotechnical change.Whether motivated to reveal or overcome dependence on infrastructure, address flaws in its design, or correct externalities generated by its use, new designers have begun to engage with the problem of infrastructure in new ways. This document analyzes these design projects through a series of case studies, synthesizing a new perspective on the study of infrastructure through design and on the scope of digital media research along the way.