The current trend in rewritable optical data storage is toward the use of novel techniques to achieve densities and data rates that are superior to those achievable in hard disk magnetic recording. After a brief review of the magneto-optical properties of amorphous rare earth-transition metal alloys, we describe the methodology and potential advantages/disadvantages of solid immersion lens (SIL), front-surface recording, magnetic super resolution (MSR), land & groove recording, and partial-response-maximum-likelihood (PRML) detection schemes. We point out the differences between magneto-optical and phase-change media, which are the contenders for the rapidly developing market in Rewritable Digital Versatile Disk (DVD) products.