Calbayog City (Waray: Syudad san Calbayog, Cebuano: Dakbayan sa Calbayog, Tagalog: Lungsod ng Calbayog) is a first class city in the province of Samar, Philippines. It lies along the coastal region of the province stretching about 60 miles (97 km) from the northern tip of the island and 180 miles (290 km) from southern boundaries. Calbayog comprises 157 barangays, 25 of which are urban and 132 are rural. According to the 2010 census, Calbayog has a population of 172,778 (37,395 households) making it the third most populated city in Eastern Visayas and the most populated city in Samar Island, the city alone makes up for 23.5% of the population of the province of Samar. Calbayog is one of the commercial trade centers in Eastern Visayas. And is the center of commerce in Samar. Its airport and a seaport make it an ideal gateway to Samar. Calbayog is subdivided into three major districts: Calbayog, Tinambacan, and Oquendo.

Calbayog's early history has been associated with the introduction and spread of Catholicism in the country. Calbayog started as one of the small settlements in the Island of Samar, an area assigned to the Jesuit missionaries. Jesuit chroniclers, as early as the 17th century, notably Fr. Ignacio Alcina, wrote many accounts about it and its people. Jesuit records and reports referred to the settlement initially as Ibatan and Jibatang (Hibatang). In the annual report of 1739 the name Calbayog appeared for the first time. Fr. de Huerta, a 19th century Franciscan writer, noted in his work Estado Geografico that in earlier times, Calbayog was called Tiayban for having been founded near a river of the same name. Then it was transferred due to a flood to the shore of the Hibatang River, whose name it took. Then again the settlers transferred to the place that they permanently occupied and took the name Calbayog.