सीन (Seine) फ़्रांस में बहने वाली एक नदी है। इसका उद्गम डीजोन (Dijon) के उत्तर-पश्चिम के कम्यून में है और यह इंग्लिश चैनल में जाकर गिरती है। इसकी लम्बाई लगभग 777 किमी है। पेरिस शहर सीन नदी के किनारे ही स्थित है।

The Seine is a 777-kilometre-long (483 mi) river in northern France. Its drainage basin is in the Paris Basin covering most of northern France. It rises at Source-Seine, 30 kilometres (19 mi) northwest of Dijon in northeastern France in the Langres plateau, flowing through Paris and into the English Channel at Le Havre. It is navigable by ocean-going vessels as far as Rouen, 120 kilometres (75 mi) from the sea. Over 60 percent of its length, as far as Burgundy, is negotiable by large barges and most tour boats, and nearly its whole length is available for recreational boating; excursion boats offer sightseeing tours of the river banks in the capital city, Paris.