This study is the first systematic review of research on outdoor learning occurring in all disciplines and interdisciplinary areas of study at higher education institutions in the United States and published in refereed English language journals. The article describes characteristics of outdoor learning research (OLR) and outdoor learning (OL). It discusses similarities, differences, challenges and trends as well as recommending additional research. The research protocol consists of a systematic search of 10 bibliographic databases using 18 keywords and 5 structural criteria to identify articles. This yielded 183 refereed articles published between 1996 and 2020 for analysis. Results and discussion are presented in seven categories. Outdoor learning research (OLR) publication frequency is growing, but is diffused among many journals resulting in limited communication of results. OLR is not a primary focus for most authors, limiting progress in understanding and development. OLR occurs at doctoral institutions and is distributed across disciplines and interdisciplinary areas. OLR is mostly descriptive, often case studies. Theory testing and inferential research is less common. Outdoor learning (OL) occurs in many academic areas with agriculture and social sciences, sustainability and adventure being most frequent. Learning methods use constructivist theory and experiential methods. Venues are diverse. OL drivers and barriers are generic and need elaboration. Enhanced learning and improved practices are stated outcomes. OL is a growing, but disjointed component of U.S. higher education. OLR demonstrates that OL addresses changing academic and participant interests. Recommendations to enhance OL practice are provided. Suggestions are made for future outdoor learning research.