Symbiotic nitrogen fixation is a crucial ecological process that is done by specialized bacteria. It plays a vital role in improving soil fertility and supporting plant growth, especially in areas where there is a lack of nitrogen. The species Casuarina is well-known for its ability to fix nitrogen through symbiotic relationships with diazotrophic bacteria, making it a prominent example of this phenomena. Comprehending the complex interconnection between Casuarina species and their nitrogen-fixing bacterial communities is essential for effectively using their capabilities in agroforestry and ecological restoration endeavors. This protocol involves a comprehensive examination of the existing knowledge about the bacterial populations that are engaged in the process of symbiotic nitrogen fixation in Casuarina sp. This chapter explains the methods used to analyze and identify bacterial populations, including traditional isolation techniques and more advanced high-throughput sequencing methods. Moreover, it explores the elements that impact the formation of variety of these bacterial populations, including host specialization, ambient circumstances, and soil qualities. This thorough evaluation highlights the significance of understanding the complex relationship between Casuarina species and their mutually beneficial nitrogen-fixing bacterial communities. The knowledge obtained from this investigation has the potential to greatly enhance the efficiency of nitrogen fixation strategies using Casuarina, leading to sustainable solutions for soil enhancement and ecosystem restoration in many ecological environments.