Estrogen receptors (ERs) are involved in regulating many complex physiological processes in the human body. Abnormal ERs signaling can lead to various diseases, including neurological disorders, osteoporosis,heart disease, and breast cancer. ERα, ERβ, and the novel G protein-coupled ER 1 (GPER-1) are considered to be the most important ERs. ERs knockout models can exhibit disease phenotypes and can serve as new animal models for studying ER-related diseases and their interventions. This paper reviews the research progress and important roles of estrogen and ERα, ERβ, and GPER-1, as well as the application of ERs knockout models in diseases.