The world is currently relying on the massive consumption of synthetic nitrogen fertilisers to maintain sufficient food production; however, this unsustainable agricultural practice is expensive and is leading to serious environmental pollution. Legume-rhizobia associated biological nitrogen fixation (BNF) via nodulation can alleviate this problem by reducing our dependence on the use of synthetic fertilisers. Therefore, a better understanding of nodule organogenesis and its regulation is important to help enhance the benefits of BNF gained from legumes. The autoregulation of nodulation (AON) process is a systemic mechanism in which rhizobia-induced CLE peptides are produced in the roots and transported to the shoots, where they induce a signal for the negative feedback of continued nodule development. Nodulation is also regulated locally by external factors, such as high soil nitrogen content. In soybeans (Glycine max), three nodulation-suppressive CLE peptide encoding genes have been identified; two elicited by rhizobium inoculation (GmRIC1 and GmRIC2) and one by nitrate treatment (GmNIC1). The rhizobium-responsive CLE genes are differentially expressed, but their overexpression results in a similar level of nodulation-inhibition. The expression of GmNIC1 is correlated with nitrate concentration, and a 50% reduction in nodule number is achieved with constitutive expression. Each of these three nodulation-suppressing genes has a duplicate copy as a result of soybean undergoing a duplication event roughly 13 million years ago. Findings regarding the extent of expression and tissue-specific activity of each of these six genes will be presented.