The early stages of the molecular self-assembly pathway leading to crystal nucleation have a significant influence on the properties and purity of organic materials. This mini review collates the work on organic mesoscale clusters and discusses their importance in nucleation processes, with a particular focus on their critical properties and susceptibility to sample treatment parameters. This is accomplished by a review of detection methods, including dynamic light scattering, nanoparticle tracking analysis, small angle X-ray scattering, and transmission electron microscopy. Considering the challenges associated with crystallisation of flexible and large-molecule active pharmaceutical ingredients, the dynamic nature of mesoscale clusters has the potential to expand the discovery of novel crystal forms. By collating literature on mesoscale clusters for organic molecules, a more comprehensive understanding of their role in nucleation will evolve and can guide further research efforts.