PURPOSE: HER2 alterations are potential candidates for targeted treatments in metastatic urothelial/bladder cancer (mUC). ERBB2 gene amplification and mutations are found in around 6% and 4% of mUC, respectively. METHODS: This is a systematic review of clinical trials evaluating HER2-targeting (amplification and mutations) in mUC. We assigned each study to one of the following strategies: HER2-targeting with single agents, anti-HER2 agents in combination with cytotoxic chemotherapy, dual HER2 blockade, HER2-targeted antibody-drug conjugates (ADCs), and other novel therapeutic approaches. RESULTS: 36 clinical trials (17 with results and 19 ongoing) were included. As for ERBB2 amplification, anti-HER2 single agents (5 studies) and combinations with chemotherapy (4 studies) failed to provide any benefit, whereas dual HER2 blockade through monoclonal antibodies proved active in one trial in pretreated patients. Two studies assessed single-agent targeting for ERBB2 mutations with negative results. Most promising data come from 2 studies with ADCs in ERBB2 amplified tumors (disitamab-vedotin and trastuzumab-duocarmazine), while 2 other studies with TDM-1 and ADCT-502 was discontinued due to toxicity. In this category, trastuzumab-deruxtecan and other ADCs are still under investigation for either ERBB2-amplified or mutated mUC. Novel approaches include ADCs with immunotherapy (1 study with results), CAR-T cells, and HER2-sensitising vaccines. CONCLUSIONS: ERBB2 amplification could become a novel target in mUC, although the magnitude of clinical benefit remains to be clarified. To this regard, novel ADCs are the most promising strategy. ERBB2 mutations are still at very early stage of clinical study.