Interstitial lung disease (ILD) is a group of disorders that are often characterized by fibrosis of the lung parenchyma, typically causing increased dyspnea, functional limitation, and early mortality. Approximately 5-25% of ILD patients cannot be provided with a confident diagnosis despite an exhaustive search for potential etiologies and a multidisciplinary review. This can occur due to an incomplete acquisition of diagnostic studies, conflicting or overlapping features, or non-classifiable histological findings. The clinical features of unclassifiable ILD have been described in several recent studies, showing that this population includes a heterogeneous collection of patients that have similar characteristics compared to mixed ILD cohorts. Pharmacotherapy for patients with unclassifiable ILD is typically guided by a multidisciplinary review that considers the most likely diagnosis and anticipated disease behaviour. The objective of this review is to summarize recent studies related to unclassifiable ILD, with a focus on its prevalence, characteristics, and outcomes. Limitations in the literature are identified, including the inconsistent terminology and lack of a precise definition of unclassifiable ILD.