Leningrad Oblast (Russian: Ленинградская область, romanized: Leningradskaya oblastʹ, IPA: [lʲɪnʲɪnˈgratskəjə ˈobləsʲtʲ]; Veps: Leningradan agj; Finnish: Leningradin alue) is a federal subject of Russia (an oblast). The oblast has an area of 84,500 square kilometres (32,600 sq mi) and a population of 2,000,997 (2021 Census); up from 1,716,868 recorded in the 2010 Census. Leningrad Oblast is highly industrialized. Its administrative center and largest city is Gatchina.

The oblast was established on 1 August 1927, although it was not until 1946 that the oblast's borders had been mostly settled in their present position. The oblast was named after the city of Leningrad. In 1991, the city restored its original name, Saint Petersburg, but the oblast retains the name of Leningrad. It overlaps the historical region of Ingria, and is bordered by Finland (Kymenlaakso and South Karelia) in the northwest and Estonia (Ida-Viru County) in the west, as well as five federal subjects of Russia: the Republic of Karelia in the northeast, Vologda Oblast in the east, Novgorod Oblast in the south, Pskov Oblast in the southwest, and the federal city of Saint Petersburg in the west.

The first governor of Leningrad Oblast was Vadim Gustov (in 1996–1998). The current governor, since 2012, is Aleksandr Drozdenko.

Leningrad Oblast is located around the Gulf of Finland and south of two great freshwater lakes, Lake Ladoga and Lake Onega. The oblast includes the Karelian Isthmus and some islands, including Gogland in the Gulf of Finland and Konevets in Lake Ladoga.

Much of the area of the oblast belongs to the drainage basin of the Neva, which is the only outflow of Lake Ladoga. The Neva, which flows to the Gulf of Finland (the city of Saint Petersburg is located in its river delta) is relatively short, but its drainage basin is very large, including Lake Onega and Lake Ilmen. The Svir and the Volkhov flow from Lake Onega and Lake Ilmen, respectively, to Lake Ladoga. Other major tributaries of Lake Ladoga include the Vuoksi and the Syas. Rivers in the western part of the oblast flow to the Gulf of Finland; the two biggest rivers there are the Luga and the Narva, which forms the border of Russia and Estonia. Small areas in the east of the oblast lie within the river basin of the Chagodoshcha, a tributary of the Mologa, and of the Suda, both within the Volga basin. A ridgeline in Tikhvinsky District in the eastern oblast forms part of the divide between the Baltic Sea and Caspian Sea basins.

The terrain of Leningrad Oblast is relatively flat and mostly covered with forest and swamps. An exception is the rocky Karelian Isthmus, which contains a lake district, as well as the Vepsian Upland in the east. The biggest lakes on the isthmus are Lake Vuoksa, Lake Sukhodolskoye, and Lake Otradnoye.

Leningrad Oblast contains two federally protected natural areas, the Nizhnesvirsky Nature Reserve and Mshinskoye Boloto Zakaznik, both created to protect the forest and swamp landscapes of northwestern Russia.

The most taxonomically diverse vascular plant families are Asteraceae, Cyperaceae, Poaceae and Rosaceae. By far the most diverse genus is Carex (68 species). The diversity in genera Hieracium (with Pilosella), Ranunculus (with Batrachium), Alchemilla, Galium, Potamogeton, Salix, Veronica, Viola, Juncus, Artemisia, Potentilla, Rumex, Festuca, Epilobium, Poa, Trifolium, Campanula, Vicia, Lathyrus, Geranium is also considerable. The territory has no endemic plant taxa. Vascular plant species of Leningrad Oblast listed in the red data book of Russia are Botrychium simplex, Cephalanthera rubra, Cypripedium calceolus, Epipogium aphyllum, Lobelia dortmanna, Myrica gale, Ophrys insectifera, Orchis militaris, Pulsatilla pratensis, Pulsatilla vernalis.