Hernals (German pronunciation: [hɛʁˈnals] ^ⓘ; Viennese: Hernois) is the 17th district of Vienna, Austria (German: 17. Bezirk, Hernals). Hernals is in northwest Vienna. It was annexed in 1892 out of the townships of Hernals, Dornbach, and Neuwaldegg.

The district of Hernals stretches out along the canals of the Als River west of Vienna between the Wienerwald (Vienna Forest) and the Gürtel (a main street around inner Vienna). The Als is the second-longest stream (the longest is the Wien River) to flow from the Wienerwald into the Danube. The highest point, at 464 meters, is Heuberg. The original Vororte of Hernals, Dornbach, and Neuwaldegg were annexed in 1892 and form the heart of the 17th district. The houses in the central areas were built around the turn of the 19th–20th centuries during the Gründerzeit. Further out, the original farmer houses remain, often with gardens and villas added on. Farmland composes about 29.7% of the land area of the district, and transportation support buildings compose about 10.3% of the area. With about 59.6% of the area populated with greenery, Hernals is one of the greenest districts in Vienna, with 39.6% forest and 14% smaller gardens and meadows. Agriculture composes only 1.4% and plays little role today. The wineries have mostly retreated into the hills of Schafberg and belong to the Roman Catholic parish of Dornbach.

The developed area of Hernals covers 29.7% (Vienna citywide: 33.3%) of the district area. The proportion of residential area in the built-space is 90.9%, the 2nd highest in Vienna. Accordingly, the proportion of farm land (2.8%) and land for the cultural, religious, sporting or public sector (5.4%), in the developed area, is limited.

Greenspace in Hernals covers 59.6%, by which Hernals is the 3rd greenest district. Nearly 66.5% of the greenspace falls in forests, 12.1% in meadows, and 11.4% in small gardens. The outdoor sports and recreation areas (3.7%) use only a small amount of Hernalser greenspace. The former major wine-growing region has all but disappeared on Schafberg hill.

The proportion of trafficked area in the district is 10.3%, very low. Waters cover 0.4% of the district area.

Archaeological digs place the first settlements in the Hernals district in the Neolithic Era, near the Als Stream, whose waters were teaming with fish. Digs from the Roman times reveal brickyards near today's Elterleinplatz. During the Middle Ages, the villages (Vororte) of Hernals and Dornbach were built along the Als, while Neuwaldegg was founded at the start of the Modern Era.

The founding of Hernals as the 17th district of Vienna came during the end of the 19th century. After the suburb cities (Vorstädte) of Vienna were annexed in 1850, discussions began in the 1870s to annex more of the surrounding areas. Although the areas were against such an annexation, Emperor Franz Joseph I declared in 1888 that it would be so. The decree took effect on January 1, 1892 and united Hernals, Dornbach, and Neuwaldegg together as the 17th district. At that time, the Hernals township was the most significant of the three and was the most populous township of Lower Austria beside Vienna.

In 1890, 74,657 people and 1,803 houses composed the newly established district. District director Kretschek and the advisor of the Hernals township Sebastian Grünbeck re-established the St. Anna Chapel, the building of the Jörgerbad spa, the building of various schools, administration of the streets, and expansions of the Hernals cemetery. In 1894, the city wall was torn down and the rail lines were built. The Hernalser Market was moved to Zimmermannplatz.