LOFAR: The LOw-Frequency ARray

LOFAR, the LOw-Frequency ARray, is a new-generation radio interferometer constructed in the north of the Netherlands and across europe. Utilizing a novel phased-array design, LOFARcovers the largely unexplored low-frequency range from 10-240 MHz and provides a number of unique observing capabilities. Spreading out from a core located near the village of Exloo in the northeast of the Netherlands, a total of 40 LOFARstations are nearing completion. A further five stations have been deployed throughout Germany, and one station has been built in each of France, Sweden, and the UK. Digital beam-forming techniques make the LOFARsystem agile and allow for rapid repointingof the telescope as well as the potential for multiple simultaneous observations. With its dense core array and long interferometric baselines, LOFARachieves unparalleled sensitivity and angular resolution in the low-frequency radio regime. The LOFARfacilities are jointly operated by the International LOFARTelescope (ILT) foundation, as an observatoryopen to the global astronomical community. LOFARis one of the first radio observatoriesto feature automated processing pipelines to deliver fully calibrated science products to its user community. LOFAR's new capabilities, techniques and modus operandi make it an important pathfinderfor the Square Kilometre Array (SKA). We give an overview of the LOFARinstrument, its major hardware and software components, and the core science objectives that have driven its design. In addition, we present a selection of new results from the commissioning phase of this new radio observatory.