The Reformed Church in Romania (; ) is a Calvinist denomination and the largest Protestant church in Romania. The majority of its followers are of Hungarian ethnicity and Hungarian is the main church language. The large majority of the Church's parishes are in Transylvania; according to the 2021 census, 495,380 people or 2.6% of the total population belong to the Reformed Church. About 95% of the members were of Hungarian ethnicity.
The religious institution is composed of two bishoprics, the Reformed Diocese of Királyhágómellék and the Reformed Diocese of Transylvania. The headquarters are at Oradea and Cluj-Napoca, respectively.
Together with the Unitarian Church of Transylvania and the two Lutheran churches of Romania (the Evangelical Lutheran Church in Romania and the Evangelical Church of Augustan Confession), the Calvinist community runs the Protestant Theological Institute of Cluj.
The church adheres to the: