with n = m/|m| being an unit vector parallel to the local magnetic moment m. [10,11] This means that the arrangement of spins within a single skyrmion can wrap a sphere nonzero integer times. The case of Φ = ± 1 is exemplified in Figure 1a, which suggests the topologically protected nature of the skyrmion spin texture.To stabilize such magnetic skyrmions, several different approaches have been proposed. For example, the interplay between the magnetic dipole-dipole interaction and uniaxial magnetic anisotropy often leads to the formation of a cylindrical magnetic domain structure termed magnetic bubble, [15][16][17][18] which is known to host various integer skyrmion numbers in cases depending on the detail of the internal spin texture. [19][20][21] The magnetic bubble was once utilized as the information carrier for magnetic storage devices (i.e., magnetic bubble memory), which was commercially available in the 1980s but later discontinued partly because the relatively large size of the magnetic bubble (≈1 μm) prevents further improvement of information density. Some latest studies suggest the possible miniaturization of bubble size down to sub-micron scale in multi-layered thin films with finely tuned magnetic parameters. [22,23] More recently, the experimental discovery of nanometric skyrmions has been reported for a series of ferromagnets with noncentrosymmetric crystal structure, where antisymmetric exchange interaction, i.e. Dzyaloshinskii-Moriya (DM) interaction, [24,25] originating from relativistic spin-orbit interaction plays a key role for the skyrmion formation. In this case, the size of skyrmion or the associated magnetic modulation period λ is determined by the ratio between the magnitudes of DM interaction D and ferromagnetic exchange interaction J in form of λ ∝ J/D, which typically ranges from 1 to 100 nm. The internal spin texture of magnetic skyrmions essentially depends on the symmetry of the underlying crystallographic lattice and associated DM interaction. [8,26] So far, most of the single-component materials showing magnetic skyrmions possess a chiral crystal structure, where Bloch-type skyrmions with a vortex-like swirling spin texture (Figure 1b) are observed. [10,12,[27][28][29][30] In contrast, under the uniaxial polar crystal structure, [31] the emergence of Néel type skyrmion with radial spin texture (Figure 1c) has been proposed. [8,26,32] Bloch (Néel) type skyrmions can form close-packed 2D hexagonal lattice (Figure 1f), which can be viewed as the superposition The concept of a skyrmion, which was first introduced by Tony Skyrme in the field of particle physics, has become widespread in condensed matter physics to describe various topological orders. Skyrmions in magnetic materials have recently received particular attention; they represent vortex-like spin structures with the character of nanometric particles and produce fascinating physical properties rooted in their topological nature. Here, a series of noncentrosymmetric ferromagnets hosting skyrmions is reviewed: B20 metals, Cu...