AbstractThe development of residual strains within a material is a valuable engineering technique for increasing the material's strength and toughness. Residual strains occur naturally in some biominerals and are an important feature that is recently highlighted in biomineral studies. Here, manifestations of internal residual strains detected in biominerals are reviewed. The mechanisms by which they develop, as well as their impact on the biominerals' mechanical properties, are described. The question as to whether they can be utilized in multiscale strengthening and toughening strategies for biominerals is discussed.