The steroid and thyroid hormone receptor superfamily plays a crucial role in transcriptional control and cell identity. These receptors, which include those for thyroid hormone and retinoic acid, are essential for development, differentiation, and physiological responses. Despite the diversity of physiological mechanisms, the discovery of receptor-related molecules in various species suggests that the mechanisms underlying morphogenesis and homeostasis may be more widespread than previously thought. Steroid and thyroid hormones act by binding to intracellular receptors, which then activate gene networks to coordinate complex developmental and physiological events. These hormone-receptor complexes are key in determining cell lineage commitment and differentiation. The review outlines the historical perspective of these molecules in gene expression regulation, the evolution of understanding their structure and function, and emerging issues in hormone action physiology. Historically, diseases linked to steroid and thyroid hormone dysfunction were identified early, and the isolation of these hormones in the early 20th century provided a foundation for physiological studies. The discovery of steroid and thyroid hormone receptors in the 1970s revealed their role in gene regulation. The purification of these receptors and the identification of hormone response elements (HREs) have advanced understanding of how these receptors activate gene expression. The steroid and thyroid hormone receptor superfamily includes a variety of receptors, such as the glucocorticoid, estrogen, progesterone, and vitamin D receptors. These receptors share structural and functional similarities, and their activation leads to the regulation of gene expression. The identification of HREs and the development of techniques to study receptor function have provided insights into the molecular mechanisms of hormone action. The structure of these receptors includes domains for hormone binding, DNA binding, and transactivation. The DNA-binding domain is highly conserved and contains cysteine residues that are critical for DNA interaction. The N-terminal region of the receptors is more variable but contributes to receptor function. The identification of these domains has led to a better understanding of how receptors regulate gene expression. The superfamily includes various subfamilies, such as the thyroid hormone receptors and the retinoic acid receptor. These receptors are involved in development and homeostasis, and their dysfunction can lead to disease. The discovery of new receptors and their ligands has expanded the understanding of hormone action and its physiological implications. The study of these receptors has revealed that they play a critical role in development and physiology. The identification of HREs and the development of techniques to study receptor function have provided insights into the molecular mechanisms of hormone action. The review highlights the importance of these receptors in gene regulation and their potential implications for disease.The steroid and thyroid hormone receptor superfamily plays a crucial role in transcriptional control and cell identity. These receptors, which include those for thyroid hormone and retinoic acid, are essential for development, differentiation, and physiological responses. Despite the diversity of physiological mechanisms, the discovery of receptor-related molecules in various species suggests that the mechanisms underlying morphogenesis and homeostasis may be more widespread than previously thought. Steroid and thyroid hormones act by binding to intracellular receptors, which then activate gene networks to coordinate complex developmental and physiological events. These hormone-receptor complexes are key in determining cell lineage commitment and differentiation. The review outlines the historical perspective of these molecules in gene expression regulation, the evolution of understanding their structure and function, and emerging issues in hormone action physiology. Historically, diseases linked to steroid and thyroid hormone dysfunction were identified early, and the isolation of these hormones in the early 20th century provided a foundation for physiological studies. The discovery of steroid and thyroid hormone receptors in the 1970s revealed their role in gene regulation. The purification of these receptors and the identification of hormone response elements (HREs) have advanced understanding of how these receptors activate gene expression. The steroid and thyroid hormone receptor superfamily includes a variety of receptors, such as the glucocorticoid, estrogen, progesterone, and vitamin D receptors. These receptors share structural and functional similarities, and their activation leads to the regulation of gene expression. The identification of HREs and the development of techniques to study receptor function have provided insights into the molecular mechanisms of hormone action. The structure of these receptors includes domains for hormone binding, DNA binding, and transactivation. The DNA-binding domain is highly conserved and contains cysteine residues that are critical for DNA interaction. The N-terminal region of the receptors is more variable but contributes to receptor function. The identification of these domains has led to a better understanding of how receptors regulate gene expression. The superfamily includes various subfamilies, such as the thyroid hormone receptors and the retinoic acid receptor. These receptors are involved in development and homeostasis, and their dysfunction can lead to disease. The discovery of new receptors and their ligands has expanded the understanding of hormone action and its physiological implications. The study of these receptors has revealed that they play a critical role in development and physiology. The identification of HREs and the development of techniques to study receptor function have provided insights into the molecular mechanisms of hormone action. The review highlights the importance of these receptors in gene regulation and their potential implications for disease.