The Cem (Albanian: Cem, or in its definite form Cemi), also known as the Cijevna (Cyrillic: Цијевна), is a river that rises in Kelmend, Albania and after nearly half of its length crosses into Montenegro, where it flows into the River Morača near the capital Podgorica.

The Cem is fully formed at the confluence of its two tributaries the Vukël Cem and the Selcë Cem. It passes mostly through limestone terrain with many karstic formations. These features of the Cem's basin have their origin in the tectonic activity of the Alpine orogeny, which formed the Dinaric Alps. The terrain through which it flows in its 58.8-kilometre (36.5 mi) course, is at an elevation of more than 1,200 m (3,900 ft) and can reach as low as 50 m (160 ft). It passes through narrow valleys and steep canyons, where waterfalls are formed before it reaches the Zeta plain. As it approaches the Morača, the Cem area shifts from a continental climate to a Mediterranean one. The drainage basin of the Cem encompasses 368 square kilometres (142 sq mi) and is part of the Adriatic river basin.

The first cultural indicators of human settlement in the Cem river basin are from the late Copper Age and early Bronze Age (3500-2300 BC). Illyrian tribes such as the Labeatae lived in the area in classical antiquity. In the following millennia, the area passed under the control of the Roman Empire and its eastern counterpart, Slavic principalities, the Republic of Venice and the Ottoman Empire. The Cem basin was the home of Albanian tribes (fise) such as Kelmendi, Hoti, Gruda and Triepshi until the 20th century. Today, the river is divided between Albania and Montenegro.

The Cem is one of the last free-flowing rivers in Europe. The river's basin is a source of very high biodiversity, and hundreds of plant and animal species live along its banks. Mammals include wild boars, brown bears and red foxes. The river's canyon is an Important Bird Area for species like the short-toed snake eagle and the Levant sparrowhawk. The marble trout is one of the 22 fish species in the river, which consistently ranks as one of the least polluted rivers in Albania and Montenegro. In the 21st century, it is threatened by industrialization, the installation of small hydropower stations and the effects of climate change in Europe.

The Greek geographer Ptolemy was the first to mention the Cem as Kinna in ancient Greek. In Tabula Peutingeriana a location named Cinna in Latin is connected to the river. These two forms are considered to be written forms of a local, Illyrian name Cinua. Albanian Cem and medieval Slavic Cenva and Cemva ultimately stem from this original name of the river. The phonological evolution of Cinua to the Albanian Cem presupposes the Slavic second palatalization. Montenegrin– and also Bosniak and Serbian – Cijevna is derived from Serbo-Croatian cijev (pipe), but other toponyms preserve the older name Ćemovsko polje (field of Cem).

The Cem originates in Kelmend, Malësi e Madhe, Albania and flows through the region of Malësia. The river has two tributaries: the Vukël Cem (Cemi i Vuklit) and the Selcë Cem (Cemi i Selcës), which join at the confluence of Tamarë. The Vukël Cem – the more important of the two in terms of water volume – rises at 900 m (3,000 ft) above sea level and flows for 17.9 km (11.1 mi). It passes through a narrow canyon, a terrain which widens only near Kozhnja, where deposition has formed a small limestone valley. A creek called the Nikç Cem (Cem i Nikçit) contributes to its volume in the rainy period. A small hydropower project has been built where the Cem i Nikçit passes through Kozhnja.

The Selcë Cem rises at 1,250 m (4,100 ft) on Mount Bordolec near Lëpushë and flows for 22.5 km (14.0 mi) mostly through narrow limestone terrain until it reaches the valley of Tamarë. In its course it passes through the Gropat e Selcës karstic caves, the canyon of Gerrlla, 900 m (3,000 ft) long and 25 m (82 ft) deep, and the 30-metre-high (98 ft) waterfall of Sllapi before reaching Dobrinjë.

The Cem then flows to the southwest for 26.5 kilometres (16.5 mi) before crossing into Montenegro, near the village of Grabom. The Albania-Montenegro border crossing is located ca. 5 km (3.1 mi) west of Grabom. In Montenegro, the river flows through the villages of Tuzi for 32.3 kilometres (20.1 mi) before it flows into the Morača, just south of Podgorica. The terrain through which the river flows in Montenegro is divided into two parts. Firstly, it forms a steep canyon and then slowly crosses into the Zeta plain, of which a part is called Ćemovsko polje after the river. On the plain, Špiro Mugoša Airport has been built between the Cem and the Ribnica to the east of Podgorica Airport. The land here has become more urbanized and industrialized.