Magnetic heterostructures of highly spin polarized materials provide opportunities for the exploration of new physical phenomena and the development of spintronic devices where both charge and spin of electrons are exploited. Materials with spin polarizat ion (P) higher than those of traditional ferromagnets (P < 45% for Fe, Co, and Ni), and especially half-metallic ferromagnets with P = 100%, are highly desirable. We describe the measurements of the intrinsic spin polarization of half-metallic CrO2 with P = 96% and the unique magnetic and other electronic properties of these single-crystal CrO2 films, epitaxially grown on TiO2 substrates by chemical vapor deposition.