Objective: To update concepts on thyroid hormones functioning in small ruminants. Materials and methods: Through available literature review from the last 50 years in the BBCS-LILACS, Fuente Academica, IB-PsycINFO, IB-SSCI, IB-SciELO, SCOPUS, and SCIRUS data bases as well as historical articles, texts and references cited in published work. Results: Information obtained related to the objectives proposed in the present review allows to classify into five sections as follows: thyroid hormones functioning; thyroid hormones and reproduction of small ruminants; thyroid hormones and fetal development; thyroid hormones, pregnancy and lactation; and factors that alter thyroid hormones levels. Conclusion: The proper functioning of metabolic pathways depends largely of thyroid hormones due to their specific effects on different organs, maintaining the homeostasis among all tissues.