Scanning probe-based memories have demonstrated their ability to store data at ultra-high densities, well in excess of 1 Tbit/sq. in.. In addition they offer the capability for relatively fast writing and reading, in excess of 1 Mbit/second/tip, combined with very low energy consumption (a few pico Joules of writing energy per bit). Thus, scanning probe-based technology would seem to offer an attractive route for the provision of ultra-compact, ultra-high density, ultra-low power memories. In this paper we discuss the three major families of probe storage: (i) probe storage using thermo-mechanical (and purely mechanical) write/read in polymer media; (ii) probe storage using electrical writing (and various readout methods) in ferroelectric media; (iii) probe storage using electro-thermal writing and electrical reading in phase-change media. We discuss the physical principles behind the writing and reading methods in each case, as well as media and (probe) tip design and fabrication issues. We also review very briefly some of the potential application areas for probe storage. (C) 2011 Elsevier B. V. All rights reserved.