A significant constraint to the development of fundamental and applied research on macroalgae is the capacity to maintain representative cultures of living material ex situ. This is also relevant for their commercial exploitation, where seasonal factors may limit the availability of seed stock for commercial-scale cultivation. Although it is technically possible to maintain clonal cultures of gametophytes and sporophytes of a range of macroalgae by routine serial transfer, logistical and security issues limit its applicability. Long-term maintenance and the stability of the material cannot be guaranteed and over time a large proportion of the less robust isolates may be lost. Cryopreservation, storage at ultra-low temperatures, in theory, obviates these problems as, assuming that the material survives the procedure and appropriate cryogenic storage temperatures are maintained, samples remain stable for hundreds of years. There is a small, but growing, literature on the application of cryogenic storage for macroalgae. However, as for other organisms, success is limited to small samples, usually around 1 mL in volume, and small life stages of the algae. This chapter provides some background to the procedures that can be employed, a brief overview of the current status of macroalgal cryopreservation, and examples of methods based on the two alternative approaches to cryopreservation are outlined. Keywords: Conservation, cryoinjury, cryopreservation, genetic resources, macroalgae, seaweed, vitrification