Ecomaterials are sustainable alternatives to traditional materials, have lower environmental impact, reduced carbon footprint, and are economically viable. Sustainable products and benign technological inventions are deeply rooted and developed, satisfying the principles of green chemistry. In this chapter, the principles of green chemistry, green nanoscience, the principles of ecomaterials and green manufacturing, bio-circular green economy, 3R and 5R concept, and life-cycle assessment methodology are discussed with relevant examples. These fundamentals are pivotal toward developing and understanding the role of ecomaterials in diverse applications like biomedicine, construction, mining, electronics, space, pharma, cosmetics, textiles, petroleum refining, and a few others. Evaluation criteria followed at different stages of product development, starting from the product design to the final product packaging, are elaborated here. In addition to ISO regulatory standards, assessment by product-focused certification bodies to prove their sustainability commitment, adherence to legal frameworks gives a big push in product/technology development from the paper trial to the commercialization.