Anisotropies in the Cosmic Microwave Background

The linear anisotropies in the temperature of the cosmic microwave background (CMB) radiation and its polarization provide a clean picture of fluctuations in the universe some 370 kyr after the big bang. Simple physics connects these fluctuations with those present in the ultra-high-energy universe, and this makes the CMB anisotropies a powerful tool for constraining the fundamental physics that was responsible for the generation of structure. Late-time effects also leave their mark, making the CMB temperature and polarization useful probes of dark energy and the astrophysics of reionization. In this review we discuss the simple physics that processes primordial perturbations into the linear temperature and polarization anisotropies. We also describe the role of the CMB in constraining cosmological parameters, and review some of the highlights of the science extracted from recent observations and the implications of this for fundamental physics.