About Book: Magnetic nanoparticles are useful for numerous applications because of their small size and their various properties based on shape and material. Long-ranged size and shape-dependent dipolar interactions provide numerous useful properties. This book describes the preparation as well as the magnetic properties of nanoparticles. 2D dots, nearly spherical samples, elongated samples, and various assemblies of nanoparticles are considered. The static magnetic structures of these nanoparticles and their dynamic properties are reported. Topological defects in 2D and 3D nanoparticles with new examples of S-shaped vortex or antivortex and of bent vortex or antivortex in 3D nanoparticles are discussed in detail. The spectrum of magnetic excitations is shown to exhibit the occurrence of gaps, a key for magnonic metamaterial devices. Magnetic excited states are also considered with their coupling to nanoparticle elastic properties.