In a number of Seyfert-1 AGN and stellar-mass black holes in binaries, X-ray spectra reveal broadened and asymmetric Fe K lines shaped by relativistic effects close to the black hole. These lines are powerful diagnostics of the inner accretion flow; they can reveal a wealth of information on the accretion disk, the nature of the hard X-ray "corona", and (most importantly) the spin of the black hole. The robustness of these lines has been questioned in the recent past, but new observations and systematic analyses reveal relativistic lines to be robust and common features. This talk will review recent progress with relativistic iron lines and discuss future directions.