CD30 is a pivotal immunohistochemical marker for the diagnosis of selected lymphoid neoplasms and an important biomarker that informs clinical consideration of CD30-targeted therapy. With the expanding clinical application of brentuximab vedotin (BV) and BV-based regimens in classical Hodgkin lymphoma, peripheral T-cell lymphoma, primary cutaneous CD30-positive T-cell lymphoproliferative disorders, and relapsed/refractory diffuse large B-cell lymphoma, the clinical role of CD30 testing has evolved beyond conventional diagnostic classification to encompass therapeutic decision-making and laboratory quality management. This review integrates the 5th edition of the WHO classification of haematolymphoid tumours (WHO-HAEM5), the International Consensus Classification (ICC, 2022), pivotal clinical trials, and recent international consensus recommendations to summarize the expression patterns of CD30 across different lymphoma subtypes, principles for immunohistochemical interpretation, standardized pathology reporting, evidence supporting CD30-targeted therapy, and key quality assurance requirements for laboratory practice. Particular emphasis is placed on the following concepts: immunohistochemistry remains the preferred method for CD30 assessment; pathology reports should adopt a descriptive approach that documents the localization, staining intensity, proportion, and distribution pattern of CD30-positive tumor cells; the clinical benefit of brentuximab vedotin is not simply correlated with the level of CD30 expression, as some patients with low-level expression or even no detectable CD30 expression by visual assessment of conventional immunohistochemistry may still derive therapeutic benefit; and standardized pre-analytical handling, quality control, interpretation criteria, review procedures, and recognition of intratumoral heterogeneity should be incorporated into routine laboratory practice. Practical recommendations regarding CD30 testing workflows, quality assurance, common diagnostic pitfalls, and pathology reporting are also provided to facilitate standardized pathology practice, laboratory quality management, and multidisciplinary clinical decision-making.