Lower Austria (Ger. Niederösterreich or österreich unter der Enns, "Austria below the river Enns"), an archduchy and crownland of Austria, bounded E. by Hungary, N. by Bohemia and Moravia, W. by Bohemia and Upper Austria, and S. by Styria. It has an area of 7654 sq. m. and is divided into two parts by the Danube, which enters at its most westerly point, and leaves it at its eastern extremity, near Pressburg. North of this line is the low hilly country, known as the Waldviertel, which lies at the foot and forms the continuation of the Bohemian and Moravian plateau. Towards the W. it attains in the Weinsberger Wald, of which the highest point is the Peilstein, an altitude of 3478 ft., and descends towards the valley of the Danube through the Gföhler Wald (2368 ft.) and the Manhartsgebirge (1758 ft.). Its most south-easterly offshoots are formed by the Bisamberg (1180 ft.), near Vienna, just opposite the Kahlenberg. The southern division of the province is, in the main, mountainous and hilly, and is occupied by the Lower Austrian Alps and their offshoots. The principal groups are: the Voralpe (5802 ft.), the Dürrenstein (6156 ft.), the ötscher (6205 ft.), the Raxalpe (6589 ft.) and the Schneeberg (6806 ft.), which is the highest summit in the whole province.
To the E. of the famous ridge of Semmering are the groups of the Wechsel (5700 ft.) and the Leithagebirge (1674 ft.). The offshoots of the Alpine group are formed by the Wiener Wald, which attains an altitude of 2929 ft. in the Schöpfl and ends N.W. of Vienna in the Kahlenberg (1404 ft.) and Leopoldsberg (1380 ft.).
Lower Austria belongs to the watershed of the Danube, which with the exception of the Lainsitz, which is a tributary of the Moldau, receives all the other rivers of the province. Its principal affluents on the right are: the Enns, Ybbs, Erlauf, Pielach, Traisen, Wien, Schwechat, Fischa and Leitha; on the left the Isper, Krems, Kamp, Göllersau and the March. Besides the Danube, only the Enns and the March are navigable rivers. Amongst the small Alpine lakes, the Erlaufsee and the Lunzer See are worth mentioning. Of its mineral springs, the best known are the sulphur springs of Baden, the iodine springs of Deutsch-Altenburg, the iron springs of Pyrawarth, and the thermal springs of Vöslau. In general the climate, which varies with the configuration of the surface, is moderate and healthy, although subject to rapid changes of temperature. Although 43.4% of the total area is arable land, the soil is only of moderate fertility and does not satisfy the wants of this thickly-populated province. Woods occupy 34.2%, gardens and meadows 13.1% and pastures 3.2%. Vineyards occupy 2% of the total area and produce a good wine, specially those on the sunny slopes of the Wiener Wald. Cattle-rearing is not well developed, but game and fish are plentiful.
Mining is only of slight importance, small quantities of coal and iron-ore being extracted in the Alpine foothill region; graphite is found near Mühldorf. From an industrial point of view, Lower Austria stands, together with Bohemia and Moravia, in the front rank amongst the Austrian provinces. The centre of its great industrial activity is the capital, Vienna (q.v.); but in the region of the Wiener Wald up to the Semmering, owing to its many waters, which can be transformed into motive power, many factories are spread. The principal industries are, the metallurgic and textile industries in all their branches, milling, brewing and chemicals; paper, leather and silk; cloth, objets de luxe and millinery; physical and musical instruments; sugar, tobacco factories and foodstuffs. The very extensive commerce of the province has also its centre in Vienna. The population of Lower Austria in 1900 was 3,100,493, which corresponds to 405 inhabitants per sq. m. It is, therefore, the most densely populated province of Austria. According to the language in common use, 95% of the population was German, 4.66% was Czech, and the remainder was composed of Poles, Slovaks, Ruthenians, Croatians and Italians. According to religion 92.47% of the inhabitants were Roman Catholics; 5.07% were Jews; 2.11% were Protestants and the remainder belonged to the Greek church.
In the matter of education, Lower Austria is one of the most advanced provinces of Austria, and 99.8% of the children of school-going age attended school regularly in 1900. The local diet is composed of 78 members, of which the archbishop of Vienna, the bishop of St Pölten and the rector of the Vienna University are members ex officio. Lower Austria sends 64 members, to the Imperial Reichsrat at Vienna. For administrative purposes, the province is divided into 22 districts and three towns with autonomous municipalities: Vienna (1,662,269), the capital (since 1905 including Floridsdorf, 36,599), Wiener-Neustadt (28,438) and Waidhofen on the Ybbs (4447). Other principal towns are: Baden (12,447), Bruck on the Leitha (5134), Schwechat (8241), Korneuburg (8298), Stokerau (10,213), Krems (12,657), Mödling (15,304), Reichenau (7457), Neunkirchen (10,831), St Pölten (14,510) and Klosterneuburg (11,595).
The original archduchy, which included Upper Austria, is the nucleus of the Austrian empire, and the oldest possession of the house of Habsburg in its present dominions.
See F. Umlauft, Das Erzherzogtum österreich unter der Enns, vol. i. of the collection Die Lander österreich-Ungarns in Wort und Bild (Vienna, 1881-1889, 15 vols.); Die österreichisch-ungarische Monarchie in Wort und Bild, vol. 4. (Vienna. 1886-1902, 24 vols.); M. Vansca, Gesch. Nieder- u. Ober-österreichs (in Heeren's Staatengesch., Gotha, 1905).