<p><strong>Background.</strong> Tannins, as polyphenolic secondary metabolites of plants, are attributed both beneficial and adverse functions when they are consumed by animals, effects that depend on the chemical structure and the concentration used. Among the beneficial properties of tannins, their ability to modulate the ruminal microbiota has been observed, reducing the populations of methanogens and methane (CH₄) emissions. In addition, effects of tannins have been observed on the performance of ruminants, attributable to tannins or the by-products of their degradation. <strong>Objective.</strong> Compile and analyze available information about the properties of tannins, their use in ruminant feeding, their effects on ruminal microorganisms, and the results obtained in the mitigation of CH₄. <strong>Methodology.</strong> A literature review was made through databases available on the web such as NCBI, ELSEVIER, Google Scholar, Oxford Academic, as well as information available in books. <strong>Main findings</strong>. In the present review, information was collected on the characteristics and properties of condensed tannins (TC) and hydrolyzable tannins (TH), their effects and adaptations in the populations of ruminal microorganisms, in addition to the effects of tannins on the metabolism of ruminants. <strong>Implications</strong>. The dose and source of tannins in the ruminant diet are decisive in the results obtained in terms of CH₄ emissions and animal response. Performance will depend on the tolerance of the animal species to the effects of each type of tannin consumed. <strong>Conclusion.</strong> A better understanding of the properties, the effects on the microbiota and on the animal metabolism, could help in the implementation of more appropriate strategies for the use of forages that can contribute to the reductions in CH₄ emissions, with a balanced approach with the production and animal welfare.</p>