Nanotechnology is a truly huge area with billions of dollars of research and development funding, and publications of thousands of papers and patents, every year. In the petroleum engineering discipline, until around 2010, research and applications development of nanotechnology have been virtually non-existent. This is because the oil and gas reservoirs are generally deep, remote from surface, and in harsh environments that exhibit extreme heterogeneities over length-scales from microns to thousands of meters. Practical implementation of nanotechnology has always been under rigorous scrutiny due to the public’s concern on its human and environmental impact, and researchers in the environmental engineering discipline have carried out comprehensive studies. Colloid and interface chemists from many branches of chemical industry and other related industries extensively carried out research and development work to generate a wide variety of multi-scale dispersions of sophisticated internal structure. The chapter also presents an overview of the key concepts discussed in this book.