Blazars are variable sources on various timescales over a broad energy range spanning from radio to very high energy (>100GeV, hereafter VHE). Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. However, most of the {gamma}-ray studies performed on Mrk 501 during the past years relate to flaring activity, when the source detection and characterization with the available {gamma}-ray instrumentation was easier to perform. Our goal is to characterize in detail the source {gamma}-ray emission, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity. We organized a multiwavelength (MW) campaign on Mrk 501 between March and May 2008. This multi-instrument effort included the most sensitive VHE {gamma}-ray instruments in the northern hemisphere, namely the imaging atmospheric Cherenkov telescopesMAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. This provided extensive energy and temporal coverage of Mrk 501 throughout the entire campaign.