Trieste (/triːˈɛst/;Italian pronunciation: [triˈɛste]  listen (help·info); Slovene: Trst, German: Triest) is a city and seaport in northeastern Italy. It is situated towards the end of a narrow strip of land lying between the Adriatic Sea and Italy's border with Slovenia, which lies almost immediately south and east of the city. Trieste is located at the head of the Gulf of Trieste and throughout history it has been influenced by its location at the crossroads of Germanic, Latin and Slavic cultures. In 2009, it had a population of about 205,000 and it is the capital of the autonomous region Friuli-Venezia Giulia and Trieste province.

Trieste was one of the oldest parts of the Habsburg Monarchy from 1382 until 1918. In the 19th century, it was the most important port of one of the Great Powers of Europe. As a prosperous seaport in the Mediterranean region, Trieste became the fourth largest city of the Austro-Hungarian Empire (after Vienna, Budapest, and Prague). In the fin-de-siecle period, it emerged as an important hub for literature and music. However, the collapse of the Austro-Hungarian Empire and Trieste's union to Italy after World War I led to some decline of its "Mittel-European" cultural and commercial importance. Enjoying an economic revival during the 1930s and throughout the Cold War, Trieste was an important spot in the struggle between the Eastern and Western blocs. Today, the city is in one of the richest regions of Italy, and has been a great centre for shipping, through its port (Port of Trieste), shipbuilding and financial services.

The Trieste is a Swiss-designed, Italian-built deep-diving research bathyscaphe ("deep boat") with a crew of two, which reached a record maximum depth of about 10,911 metres (35,797 ft), in the deepest known part of the Earth's oceans, the Challenger Deep, in the Mariana Trench near Guam, on 23 January 1960, crewed by Jacques Piccard (son of the boat's designer Auguste Piccard) and U.S. Navy Lieutenant Don Walsh achieving the goal of Project Nekton.

Trieste was the first manned vessel to have reached the bottom of Challenger Deep. The vessel is on display in the parking lot of the U.S. Naval National Undersea Museum, right next to the Naval Undersea Warfare School in Keyport, Washington.

The Trieste was designed by the Swiss scientist Auguste Piccard and built originally in Italy. His pressure sphere, composed of two sections, was built by the company Acciaierie Terni, and the upper part was manufactured by the company Cantieri Riuniti dell'Adriatico, in the Free Territory of Trieste (on the border between Italy and Yugoslavia); hence that name was chosen for the bathyscaphe. The installation of the pressure sphere was done in the Cantiere navale di Castellammare di Stabia, near Naples. The Trieste was launched on 26 August 1953 into the Mediterranean Sea near the Isle of Capri. The design was based on previous experience with the bathyscaphe FNRS-2, also designed by the Piccards. (It was built in Belgium). Trieste was operated by the French Navy. After several years of operation in the Mediterranean Sea, the Trieste was purchased by the United States Navy in 1958 for $250,000.