One hundred fifty years ago, Texas was very different. A rural population was spread thinly across the eastern and central parts of the state, and vast lands in the western regions were still undisturbed. Texas's habitats and biota changed dramatically as its population increased and people spread across the landscape. In Texas Natural History: A Century of Change (2002), David Schmidly chronicled the changes that occurred during the twentieth century. In this second edition, Schmidly is joined by colleagues Robert and Lisa Bradley of Texas Tech University to extend that story over the first two decades of the twenty-first century. The focus of Texas Natural History in the 21st Century continues to be on the mammalian fauna of the state, and it includes a reprinting of Vernon Bailey's 1905 "The Biological Survey of Texas" with new annotations and updates. In the rest of the book, the authors discuss changes in landscapes, land use, and the status of Texas mammals in the last hundred years. The authors present current challenges to conserving the natural history of Texas and suggest long-term solutions to those challenges, including actions focused on both private and public lands. As Texas approaches the daunting challenge of conserving its wildlife, Texas Natural History in the 21st Century serves as a rallying cry for addressing the scenarios imperiling Texas's natural history in our present day and in the future.