Four technologies are going to rule the world in the 21st century of which the first three are biotechnology, technology of photonics and genetic engineering which had shocked the world with their new findings in the late 90’s. Nanotechnology is the fourth one which has the additional advantage of being interdisciplinary to the first three. Nanotechnology deals with the phenomena and structures that can only occur at the nanometer scale. Magnetic nanomaterials have become the topic of interest nowadays due to its unique application potential in versatile fields including high density storage media, magneto-optical display devices etc, due to their very high surface area. The optical and magnetic properties are modified greatly upon size reduction. Here two different templates have been chosen to study the non-interacting magnetic nanosystems, nanomagnetic composite and ferrofluids(stable colloidal suspension of nanomagnetic materials in a base fluid) . Thus the book has two parts, one deals with the magnetic nanocomposites, their magnetic and optical properties while the latter part describes the properties of ferrofluids. Book contains 8 chapters.