Electrically tunable liquid crystal (LC) lenses have been studied for over 30 years. Three main problems of LC lenses hinder the applications: 1) the paradox between the response time and tunable focusing range, 2) polarization dependency, and 3) large aperture size for ophthalmic lenses. In this paper, we introduce the two mode switching method of the LC lenses to solve the paradox of the LC lenses. The basic optical principles for designing polarization independent LC lenses are discussed and several polarizer-free LC lenses we developed are reviewed. Several applications of LC lenses are also introduced, including auto-focusing imaging systems, auto-focusing projection systems, optical zoom systems, endoscopic systems, solar cells, ophthalmic lenses for myopia-presbyopia.