Monotectic alloys or alloys with a miscibility gap in the liquid state are a broad kind of materials. Many of them have great potential applications in industry. However, these alloys have an essential drawback that the miscibility gap poses problems during solidification. When a homogeneous single phase liquid is cooled into the miscibility gap, the components are no longer miscible and two liquid phases develop. Generally, the liquid-liquid decomposition begins with the nucleation of the minority phase droplets. These droplets grow and coarsen then. They can also settle or float due to the specific gravity differences between phases and migrate due to the temperature gradient or concentration gradient. The motions of the droplets cause the formation of a microstructure with serious phase segregation. Researchs have been carried out to investigate the solidification process of monotectic alloys on ground as well as under the microgravity conditions in space. The feasibility of controlling the microstructures of monotectic alloys by using electric field, magnetic field, microalloying, etc. has been investigated. Meanwhile, plenty of efforts have been made to model and simulate the microstructure evolution of monotectic alloy during the L-L phase transformation. This article will review the research work in this field during the last few decades and propose some perspectives for future studies on the solidification process of monotectic alloys.