Lošinj (pronounced [lɔ̌ʃiːɲ]; Italian: Lussino; Venetian: Lusin, earlier Osero; German: Lötzing; Latin: Apsorrus; Ancient Greek: Ἄψωρος) is a Croatian island in the northern Adriatic Sea, in the Kvarner Gulf. It is almost due south of the city of Rijeka and part of the Primorje-Gorski Kotar County. The settlements on Lošinj include Nerezine, Sveti Jakov, Ćunski, Artatore, Mali Lošinj and Veli Lošinj. A regional road runs the length of the island; ferry connections (via the island of Cres) include Brestova - Porozina, Merag - Valbiska, Mali Lošinj - Zadar and Mali Lošinj - Pula. Lošinj Airport is on the island.== In film

Lošinj is part of the Cres-Lošinj archipelago. The Cres-Lošinj archipelago includes the two major islands Cres and Lošinj, some minor islands Unije, Ilovik, Susak, Vele Srakane, Male Srakane and a number of uninhabited small islets and outcrops. Cres is the largest by area, followed by Lošinj. Cres and Lošinj are connected by a small bridge at the town of Osor on Cres. The highest elevations are the mountains Televrin (also called Osoršćica) at 588 m (1,929 ft) and Sv. Nikola (also called Sv. Mikul) at 557 m (1,827 ft). The towns of Nerezine and Sveti Jakov lie at their base. The island bedrock is formed predominantly of chalk limestone and dolomite rocks. There are sand deposits in the western part of the Kurila peninsula.

Lošinj is the 11th largest Adriatic island by area, 33 km (21 mi) long, with the width varying from 4.75 km (2.95 mi) in the north and middle of the island, to 0.25 km (0.16 mi) near the town of Mali Lošinj. The total coastline of the island is 112.7 km (70.0 mi).

The island has a mild climate and evergreen vegetation (like myrtle, holm oak, and laurel). Veli Lošinj, Čikat and the south-west facing shores are ringed by pine forests, while the highest elevations in the north of the island have more sparse vegetation.

Around 2600 sunshine hours a year make the island a popular tourist destination in the summer months, especially for nearby Slovenian, German and Italian visitors. On average humidity is 70% and temperatures average 24 °C (75 °F) in the summer and 7 °C (45 °F) during the winter.

As with other locations on the Adriatic, Losinj is prone to a variety of Winds. The Bura is a north-easterly wind that brings low temperatures and dry air masses from the continent, sometimes the gusts are strong enough to turn over heavy vehicles. The Jugo is a southerly wind that originates in the Sahara, however, over the relatively long fetch over the warm waters of the Mediterranean it becomes moisture-laden, and typically brings much cloud and stormy weather. Traditionally, it is reputed to cause headaches, melancholy and even bouts of madness in the inhabitants of the coastal areas, especially Dalmatians.

The island forms part of the Kvarner Islands Important Bird Area (IBA), designated as such by BirdLife International because it supports significant numbers of many bird species, including breeding populations of several birds of prey.

Settlement on nearby Cres is known to date back around 12,000 years, and the island of Lošinj is also thought to have been inhabited since prehistoric times. This is evidenced by hill-forts at the foot of Osoršćica and around the port of Mali Lošinj. According to Ptolemy, the Romans called this island Apsorrus (Ancient Greek: Ἄψορρος), and referred to the islands of Lošinj and Cres collectively as Apsirtides. In several places, ruins of Roman villas have been excavated (villae rusticae: Liski, Sveti Jakov, and Studenčić near Ćunski). Several small eremitic churches dating from the Roman era have been preserved (St. Lovreć near Osor, and St. James in Sveti Jakov).In the Middle Ages, Lošinj was the property of the clerical and secular nobility of Osor and unpopulated.