The Athermalization tag focuses on design approaches that keep optical performance stable across changing temperatures, a critical concern for outdoor, aerospace, and industrial systems. Articles associated with this tag explain how careful selection of glass and structural materials, combined with mechanical design strategies, can minimize focus shifts and aberration changes as components expand or contract. Topics may include passive athermalization using complementary thermal properties, active approaches with focus adjustment, and the use of spacers or mounts tailored to compensate for thermal effects. These resources help readers understand how to analyze temperature sensitivity and incorporate athermal design from the earliest stages of a project rather than relying on late-stage fixes. For engineers working on infrared cameras, telescopes, metrology tools, or automotive and defense optics exposed to wide temperature ranges, this tag offers practical insight into maintaining image quality and calibration stability. It also reflects Avantier’s experience in designing and manufacturing athermalized optical assemblies that perform reliably in real-world environments.