Gram-positive bacteria have a distinct cell wall structure and are phylogenetically placed within two phyla, the Firmicutes and Actinobacteria, which are ubiquitous in nature. Although since the discovery of the denitrification process numerous Gram-positive denitrifiers have been identified, they remain underexplored compared to their Gram-negative counterparts, mostly because of the absence of the trait in model organisms like Bacillus subtilis and the high sequence divergence of their denitrification genes leading them to be undetected in the environment. This chapter focuses on the current understanding of denitrification in endo-spore forming bacilli, which appears to be membrane bound and involves new enzymes or enzyme organisations. Old and more recent insights into N2O emission by non-denitrifying bacilli are also highlighted, as this might be another highly undervalued trait that is often confused with denitrification. Finally, the methodological issues hampering the assessment of the environmental abundance and importance of denitrifying bacilli are also explored.