Associative symbiotic nitrogen fixation is a key source of a growth-limiting nutrient to plants in areas that lack leguminous or actinorhizal plants. Nitrogen fixing microbes, living as epiphytes or endophytes on plants such as perennial grasses, conifers, or bryophytes, can be the largest source of new nitrogen to their host plants and, in some cases, their ecosystems. In this session, we seek to look at non-leguminous nitrogen fixation from several different perspectives: through the host plant, the microbiome, and measurements of fixation activity. Utilizing increasingly accessible isotopic and genomic tools, scientists can now begin to answer questions about the nature of the symbiosis between host plants and associative nitrogen fixing microbes as well as investigating environmental sources of rate variation, which can help predict how nitrogen inputs will change along with climate.