Why should we investigate thyroid hormone economy and action? Many current clinical practices for diagnosing and treating patients with hypothyroidism, hyperthyroidism, or thyroid cancer are based on laboratory findings by scientists studying the fundamental aspects of thyroid hormone homeostasis. Over the last century, investigators have utilized animal, cell culture, experimental, and biochemical models to achieve milestone discoveries that have formed our understanding of thyroid physiology and disease. However, we still need to understand many biological processes regulated by thyroid hormones and how these processes relate to thyroid diseases. For example, how compromised (if at all) is thyroid hormone transport in the different neural cells of patients with MCT8 deficiency? In what ways do hormonal disruptors affect thyroid hormone signaling? Which clinically relevant biomarkers can aid in diagnosing or managing thyroid diseases? In order to answer these questions, scientists can use new methodologies to investigate the cellular and molecular biology of the hormone. This Methods Collection will highlight recent advances in animal and cellular models, as well as analytical techniques applied to the physiological biology of thyroid hormones. The toolkit presented here can help unravel new mechanisms of thyroid hormone economy and action, which is critical for developing new interventions for patients with thyroid diseases.