Soil represents the most biodiverse terrestrial ecosystem on the planet, with millions to billions of microbes present in a single gram of soil (Nielsen et al., 2015, Trevors, 2010). Only a few of these organisms have been identified, with little known about most microbes that exist in soil. Respiration measurements offer the ability to quantify and understand soil microbial activity in different ecosystems and contexts. For this reason, respiration-based procedures are gaining broad interest as part of comprehensive soil health analyses. New and adapted methodologies are likewise being developed to make use of readily available and inexpensive tools, as opposed to specialized laboratory equipment. Nonetheless, there is continued discussion regarding the underlying mechanisms and interpretation of many of these tests. Moreover, even when performed under controlled laboratory conditions, some of these tests have greater experimental uncertainty than other soil testing methods (e.g. nutrient analyses), with intra-laboratory variability identified as a major challenge (Wade et al., 2018). New advances in application and knowledge are therefore needed to fully realize the potential of these techniques. In this chapter, we review the history and basis of many of the most commonly used respiration-based methods to assess soil microbial characteristics, address some of the most critical challenges and uncertainties, and discuss future needs and trends in soil respiration research.