The coronavirus spike protein is a multifunctional molecular machine that mediates viral entry into host cells. It consists of two domains: S1, which binds to host receptors, and S2, which facilitates membrane fusion. The spike exists in two conformations: prefusion and postfusion. The transition from prefusion to postfusion is triggered, leading to membrane fusion. This review discusses the structure and function of coronavirus spike proteins, focusing on receptor recognition and membrane fusion. It also explores the evolution of these functions in the context of other viruses and host cells. Coronaviruses recognize different receptors, such as ACE2, APN, and DPP4, through their S1 domains. The S1-NTD and S1-CTD domains play critical roles in receptor recognition. The S1-CTD is involved in membrane fusion and has evolved to recognize different receptors. The spike protein's structure and function have evolved to adapt to new environments and host ranges. The spike protein's ability to recognize different receptors and undergo conformational changes is crucial for viral entry and transmission. Understanding the structure and evolution of the spike protein is essential for developing strategies to combat coronaviruses.The coronavirus spike protein is a multifunctional molecular machine that mediates viral entry into host cells. It consists of two domains: S1, which binds to host receptors, and S2, which facilitates membrane fusion. The spike exists in two conformations: prefusion and postfusion. The transition from prefusion to postfusion is triggered, leading to membrane fusion. This review discusses the structure and function of coronavirus spike proteins, focusing on receptor recognition and membrane fusion. It also explores the evolution of these functions in the context of other viruses and host cells. Coronaviruses recognize different receptors, such as ACE2, APN, and DPP4, through their S1 domains. The S1-NTD and S1-CTD domains play critical roles in receptor recognition. The S1-CTD is involved in membrane fusion and has evolved to recognize different receptors. The spike protein's structure and function have evolved to adapt to new environments and host ranges. The spike protein's ability to recognize different receptors and undergo conformational changes is crucial for viral entry and transmission. Understanding the structure and evolution of the spike protein is essential for developing strategies to combat coronaviruses.