In spite of the widespread trend of e-book adoption by U.S. academic libraries, interlibrary loan (ILL) of e-books is significantly lagging behind because of license agreement restrictions, unstandardized platforms, library policies, and technological barriers. More recently, the long-cherished tradition of ILL has been further challenged, because an increasing number of academic libraries are adopting user-based e-book purchasing models that have the potential to bypass ILL. This paper compares the findings of two longitudinal surveys on e-book ILL practices in U.S. academic libraries, based on random sampling. The results from inferential statistical analyses reveal that, while inter-library lending of entire e-books is seldom practiced and shows no growth, e-book chapter ILL is becoming more prevalent in U.S. academic libraries. Librarians have grown more knowledgeable about licensing and technological issues, but their perceptions of these barriers are mixed. The study also shows that larger institutions are more likely to perform e-book ILL services, and their librarians tend to be more positive about the future of e-book ILL.