The LHCb Collaboration is currently in the final stage of constructing an upgraded detector that will allow the experiment to operate at higher luminosities and with a triggerless readout. The main tracking stations—which originally were subdivided in an Inner Tracker made from silicon strip sensors and an Outer Tracker built from straw-tubes—are being replaced by a single tracking detector, the Scintillating fibre Tracker (SciFi). The SciFi covers a total detector area of 340 m2 by using more than 10000 km of scintillating fibre with 250 μm diameter, enabling a spatial resolution of better than 100 μm for hits originating from charged particles. It is built from individual modules (0.5 m × 4.8 m) comprised of 8 scintillating fibre mats with a length of 2.4 m as the active detector material. The 13 cm wide fibre mats consist of 6 layers of densely packed blue emitting scintillating fibres. The scintillation light is detected with arrays of multi-channel silicon photomultipliers (SiPMs) cooled to −40̂C to minimize the expected high dark noise from neutron radiation. The readout of 524k channels occurs through custom-designed front-end electronics. Since it is the first time that this technology is being used as a large tracker and with a small granularity, many challenges have to be overcome. This document is intended to give an overview of the SciFi detector design, production, performance and the status of the detector assembly.