Ferroelectricity is a spontaneous polarization state possessed by dielectrics, which generally occurs in crystalline (solid) material systems with low symmetry. Fluid or highly fluid soft matter systems usually exhibit high symmetry, which is contrary to the requirement of ferroelectricity. The introduction of strong polarity or ferroelectricity is a strategy that has attracted much attention in the fields of new liquid crystal materials and flexible optoelectronic devices. Compared with the traditional liquid crystals and soft matter systems, the ferroelectric nematic liquid crystals possess several revolutionary properties, including ultra-high dielectric permittivity, strong nonlinear optical response, low-voltage driving and high fluidity. It provides numerous possibilities for the development of novel advanced flexible optical and electronic devices. This review looks back the history of the foundation and development of the ferroelectric nematic liquid crystals, then, explains the relationship between the ferroelectric nematic liquid crystals and the molecular structure, physical topology, and characteristic properties. Finally, this review summarizes and makes a short perspective on the future applications by employing the ferroelectric nematic liquid crystals. The ferroelectric nematic liquid crystals have great potential in new memory devices, flexible high-end optoelectronic devices, nonlinear optics, and other fields.