CMB polarization anisotropies contain contributions from Cosmological Gravitational Waves and Gravitational Lensing, dominating a small, still largely unknown, component known as Bmodes. We discuss the scientific implications of these measurements for the physics of the very early Universe and the Dark Matter and Energy, respectively. We review the current knowledge on B-mode data analysis and the main efforts in EU and US for achieving accurate measurements on all accessible angular scales in the forthcoming years.