The paper highlights the role of communities of monks and nuns (the Third Orders) inthe structure and activity of the Ukrainian Greek Catholic Church (UGCC), which functionedunderground. It is emphasized that the historical roots of the Third Order are traced back to the13th century when spiritual life of specific lay communities was regulated by the Franciscan andthe Dominican Orders, and later, by the Carmelite Order. Between 1900 and 1930s lay communitiesof the UGCC became noticeably active. A characteristic example of their activity is the well knownRules for laypersons of the Basilian Order drawn by Metropolitan Archbishop Andrey Sheptytsky.In the 1970s (the Soviet time, when the UGCC worked underground), there appeared theRedemptorist and the Basilian Third Orders in Ivano-Frankivsk Oblast. Their members kept insafety different cult objects, held underground Divine Services, meetings, had spiritual practices,did catechesis, etc. On the whole, these lay communities had played an important role in theUGCC underground activity up till the late 1980s