© 2019 Elsevier Inc. Purpose: To achieve consensus amongst speech-language pathologists (SLPs) on the categories and definitions of preschoolers’ communication impairments. Methods: In Phase 1, impairments were identified, categorized, and defined based on an evidence review. In Phase 2, a four-round Modified Delphi study was completed with SLPs (N = 38). SLPs reviewed three documents that categorized and defined preschoolers’: (1) broadly focused impairments, (2) language disorder sub-categories, and (3) speech sound disorder sub-categories; rated whether categories captured all preschoolers with communication impairments and definitions were clear (consensus = 90% agreement across all documents); and made suggestions for improvement. Documents were revised between rounds based on SLPs’ responses, literature review, and consultation with experts. Results: In Round 1, 90% agreement was reached only for the language disorder sub-categories document. In Round 2, no consensus was reached for the Speech Sound Disorder sub-categories document. In Round 3, consensus was reached for all three documents, but a fourth round was run to incorporate newly updated terminology. In Round 4, consensus was reached for updated terminology presented in the language disorders document. Conclusions: Clinical and research expertise are integrated throughout the final documents, resulting in consensus terminology for preschoolers’ communication impairments. Findings can support consistent terminology for preschoolers with communication impairments amongst SLPs. In research, documents will be used in a developing data collection tool that will undergo reliability testing prior to use in large scale studies related to children's communication. This study demonstrates the value of engaging in practice-based research.