Second generation gravitational wave interferometers should detect signals from tens of coalescing compact binaries per year. In this talk we report on measurability of stellar mass black hole spins using gravitational waves. In fact, while neutron stars are expected to have small spins, black holes may have close to maximal spins. We will see how spin magnitude can often be measured with precision below 10%, and we discuss which factors impact this measurement. Finally, we will show how gravitational waves can be used to verify if spins of black holes in binaries are preferentially aligned with the orbital angular momentum, which may give important insights in the formation channels of compact binaries.