Wildfires disturb ecosystem nitrogen (N) cycling and increase soil emissions of nitric oxide (NO) and nitrous oxide (N2O) by changing soil physicochemical properties and altering microbial processes like nitrification and denitrification. In chapter 1, I synthesize 34 studies that measured NO and N2O emissions after fire and found significant increases across ecosystems globally. Fire increased soil N2O emissions in forests, NO emissions in grasslands, and increased both NO and N2O emissions in shrublands. In chapter 2, I hypothesize that shrubland NO and N2O fluxes are driven by soil burn severity and the availability of inorganic N substrates (ammonium; NH4+ and nitrate; NO3-), microbial biomass, and pH in California chaparral. I found that soil NO emissions increased for up to three years after the Holy Fire was extinguished in the Cleveland National Forest due to changes in soil N availability, microbial biomass, and pH. Fire also increased the heterogeneity of soil emissions of N2O and generated hotspots of N2O production. In chapter 3, I investigate nitrification and denitrification processes by comparing pre- and post-fire soils from the KNP complex fire in Sequoia National Park, CA. The rate-limiting step of nitrification is mediated by ammonia-oxidizing bacteria (AOB) and archaea (AOA) which oxidize NH4+ to NO3- and release NO and N2O as byproducts. Since AOB are associated with higher NO and N2O emissions and can be favored by higher soil pH and NH4+, I hypothesize increasing emissions with AOB abundance after fire. I also expected abundant NO3- to stimulate denitrification accompanied by fire-induced changes in the major microbial groups responsible for producing N2O. To test these hypotheses, I measured the activity and abundance of AOA and AOB communities and characterized the isotopic composition of N2O. I found that fire increased the abundance of AOB as expected, however, soil emissions of NO and N2O derived from AOA, AOB, and heterotrophic nitrification all increased after fire. Isotopic characterization of N2O revealed shifts in contributions from denitrifying microbial groups and increases in N2O reduction. Overall, fires affect N cycling by changing soil chemistry, altering nitrifier communities, and accelerating denitrification to elevate gaseous N losses.