AstroLink extracts meaningful hierarchical structure from astrophysical data sets. This general purpose clustering algorithm rarely requires parameter tuning before application and is readily capable of finding an arbitary number of arbitrarily shaped clusters (and their structural relationship within the broader hierarchy) from arbitrarily defined data sets. The package includes a small number of intuitive-to-adjust parameters should they be necessary. Clusters found by AstroLink are defined as being statistically distinct overdensities when compared to their surrounds and to the noisy density fluctuations within the data set.