The article summarises results of research in the field of polymethacrylate (PMMA) gel electrolytes. The prepared materials exhibit sufficient ionic conductivity (up to 2.5·10^-3 mS cm^-1), high electrochemical stability and high optical transparency. PMMA gel electrolytes are freeze-resistant down to 25 °C. The described electrochemical and material properties allow their applications in many areas such as in electrochromic devices, lithium-ion batteries, supercapacitors, and solid-state electrochemical sensors. A new, all-solid reference PMMA-Cd-Cd(ClO₄)₂ electrode was introduced for electrochemical measurements in solids and polymer gel electrolytes as well as in an electrochemical sensor for hydrogen fluoride. To improve ionic conductivity and electrochemical stability a combination of polymer gel electrolytes with ionic liquids based on 1-methylimidazole was suggested.