We have investigated the spin dependence of the potential between heavy quarks in full lattice QCD, including the effects of light quark loops. The form of the spin-orbit, the tensor and the spin-spin forces present clear evidence for long-range scalar confinement supplemented by a Coulomb force at short distances. This agrees with observations from quarkonium spectroscopy. The QCD simulation has been carried out for Kogut-Susskind fermions with four degrees of freedom at a gauge coupling β = 5.35 and a quark mass amq = 0.01 on a 163 × 24 size lattice. This corresponds to a lattice spacing 0.12 fm, a spatial lattice size of about 2 fm and a light quark mass of 48 MeV.