A fishing line is a flexible, high-tensile cord used in angling to tether and pull in fish, in conjunction with at least one hook. Fishing lines are usually pulled by and stored in a reel, but can also be retrieved by hand, with a fixed attachment to the end of a rod, or via a motor.

Fishing lines generally resemble a long, ultra-thin rope, with important attributes including length, material, weight and thickness. Other factors relevant to certain fishing environments include breaking strength, knot strength, UV resistance, castability, limpness, stretch, abrasion resistance, and visibility. Traditional fishing lines are made of silk, while most modern lines are made from synthetic polymers such as nylon, polyethylene or polyvinylidene fluoride ("fluorocarbon") and may come in monofilament or braided (multifilament) forms.