Groundwater allocation is a key institutional instrument for restoring sustainability in overdrawn aquifers, especially those that have been used on an open-access basis in the past. Many suggestions for improving groundwater management - pumping reductions, fees on overuse, transferability of pumping rights or shares - are based on the establishment of groundwater allocations. Therefore, how groundwater allocations can be created and maintained is a critical foundational issue in sustainable water resource management. In this chapter, we review the institutional and policy issues associated with establishing groundwater allocations: how they differ from and relate to allocations of surface water; the various values to be taken into account when developing allocations; and why the allocation of groundwater is an inescapably political process. We also review examples of groundwater allocation efforts and identify some patterns among those examples. Combining the review and the examples, we present and explain a set of considerations regarding the process of establishing groundwater allocations. Our considerations are intended to be useful to practitioners as well as researchers interested in this subject, and therefore potentially beneficial in practical ways in the advancement of water sustainability.