My dissertation uses natural gas and its attendant technologies to explore how interactions between human and non-human factors produced Iranian modernity in the second half of the twentieth century. In contrast to a historiography that emphasizes intellectual and political themes, I argue that the accidental abundance of natural gas within Iran's borders has resulted in a modern society ordered around its production, transportation, and consumption. Natural gas both reflected the hopes of Iranians and constrained what was possible with its physical and technical properties. I first study the expectations of Iranian planners for natural gas and the "dance of agency" between human and technical elements that marked the construction of the country's gas network. I then turn my attention to the ways that Iranians made natural gas part of their everyday lives, highlighting how consumer choice influenced Iranian modernization. Interwoven throughout are analyses of the environmental contexts that shaped people's actions. Between the early 1960s and the late 1990s, state policy, the work of local and foreign firms, and shifting social norms transformed natural gas from a waste product into the primary energy source of Iranian society. The roughly chronological chapters of this dissertation trace the story from the construction in 1963 of a small pipeline in the south of Iran, to the adoption of gas stoves during the 1970s, to the move from canister gas to gas lines in the 1980s. An epilogue explores the ongoing effort to convert Iranian vehicles from gasoline to liquefied natural gas. Natural gas systems enable an exploration of Iranian modernization that spans the caesura of the 1979 revolution and brings together the social, political, commercial, and environmental histories of the country. My research thus explores the boundaries between the social and material worlds of Iran, seeking to bring to prominence the physical contexts within which societies develop.