Manipulating the spin degrees of freedom of atomic vapors has in recent years led to exciting advances in atomic physics and quantum metrology. In particular, understanding spin relaxation phenomena in collision-dominated atomic vapors, like cesium vapors used in atomic clocks, has lead to novel ultrasensitive magnetometers, having a number of applications, from low-field NMR to biomagnetic imaging. One of the fundamental limitations of this kind of precision measurements is spontaneous spin noise. This is a quantum fluctuation of the atomic vapor’s collective spin driven by atomic collisions, and sets the noise level and hence the precision of all relevant spin measurements.