The population and their civilization in the contemporary era of science and technology are contributing to an increased environmental burden due to the excessive consumption of materials and energy. This rise in environmental load is adversely affecting the sustainability and quality of life on Earth. Therefore, the reduction of environmental load has become a crucial factor for the sustainable development of life on our planet. Ecomaterials represent a highly promising solution to mitigate the environmental load, facilitating a harmonious relationship between life and the environment. Materials that do not harm the environment in terms of their production, usage, and disposal are classified as ecomaterials. Nowadays, both nanoscience and nanotechnology play significant roles in scientific research and development, owing to their current and potential future applications in the fabrication of ecomaterials. Iron and iron oxide-based nanomaterials are particularly important as ecomaterials, offering a wide range of applications, including catalysis, photosynthesis, water remediation, biomedical uses, metallurgy, and magnetic materials. The controlled fabrication of iron and iron oxide-based nanomaterials, with respect to size and surface chemistry, is essential for their diverse applications. This chapter mainly summarizes the fundamental chemistry, fabrication processes, and applications of iron-based nanomaterials.