Two-dimensional (2D) ferromagnets with rich electronic and optical properties are crucial for scientific research and technological development, which lead to new applications in magnetic, magnetoelectric and magneto-optic devices. However, the lack of room-temperature 2D ferromagnets has greatly hindered the development of this field, such as the quantum anomalous Hall effect and thin-film spintronics. In fact, within the isotropic Heisenberg model with finite-range exchange interactions, low-dimensionality is shown to be a barrier for ferromagnetism. However, low-dimensionality at microscale patterning could improve the Curie temperature (T_C) of 2D ferromagnets with regard to bulk materials, opening the door for designing high-temperature ferromagnetic materials at the 2D limit. In this paper, we review recent advances in the field of 2D ferromagnets, including their atomic structures, physical properties, and potential applications, and highlight the strategies to enhance ferromagnetism. Our proposed directions are expected to be helpful to explore novel 2D ferromagnetic families, which not only spawn new technologies but also improve the fundamental understanding of this fascinating area.