Sergiyev Posad (Russian: Се́ргиев Поса́д) is a city and the administrative center of Sergiyevo-Posadsky District of Moscow Oblast, Russia. The city grew up around the greatest of Russian monasteries, the Troitse-Sergiyeva Lavra or "Trinity". The town became incorporated in 1742. As its name had strong religious connotations, the Soviet authorities changed it to Zagorsk (in memory of the Russian revolutionary Zagorsky) in 1930. The original name, literally meaning "Sergius' settlement" and alluding to St. Sergius of Radonezh, came back into official use in 1991. According to the 2002 Census, the town had population of 113,581, down from 114,696 recorded in the 1989 Census).

Tourism associated with the Golden Ring plays a role in the regional economy. There is also an important factory of toys.

In 1947, the Soviet Union established its first factory to weaponize smallpox at the edge of Sergiyev Posad.

The Moscow – Yaroslavl railway and highway pass through the town. Sergiyev Posad Bus Terminal is located in the city.

Main points of interest: The Trinity Monastery of Sergiev Posad was founded around 1345 by Sergei Radonezh. Three hundred and sixty years ago Polish invading forces plunged the territory of western and central Russia in a sea of anarchy, terror and fire. All the towns suffered, most of them taken and looted by the invaders. The Fortress of the Trinity Monastery alone stood firm, like a little island in the inundated land. It was heroically defended mainly by the peasants of nearby villages against invasion armies twenty times their own number. And the Russian people won after withstanding a 16-month siege. The Polish troops retreated in disgrace from the monastery grounds. The little fortress of Sergiev Posad thus became the forerunner of the hero-towns of the Patriotic War. There are 11 towers with two entrance gates erected in 1550. The main entrance to the monastery was through the Pilgrim Tower gates on the north side of the wall. The focal point of the Monastery is the white-stone Trinity Cathedral (1422) where the relics of St.Sergius are kept. The iconostasis of the cathedral contains paintings by the finest Russian icon-painter Andrei Rublev. The simple-lined, five-domed Dormition Cathedral (1570) is the monastery's official church with its beautiful frescoes of the 17th century and a huge, carved icinistasis with platforms for the choir. At the north-west corner of the Cathedral there is a burial vault of the Tsar Boris Godunov's family. The spacious Palace was used a stop-over residence of Tsar Alexei Romanov. The 300-year old Refectory with fine paintings and sculptors also worth visiting. The recently restored red and white Church of St. Zosima and Savvaty (1638) attached to the Hospital is the only tent-roofed church in the Monastery.The elaborate Metropolitan's (Rusian church Patriarch) Residence was built in the 18th century. The graceful Virgin of Smolensk Church (also of the 18th century) decorated in the magnificent baroque fashion. The finely carved Piatnitskaya Chapel and the cheerful-looking Chapel-over-the-Well were both built in 1547. The Church of the Holy Ghost was built of brick in 1476 by stone-masons from Pskov. It is an unusual type of ecclesiastical building with the bell-tower under the dome.