We study multi-quark (3Q,4Q,5Q) systems in lattice QCD. We perform the detailed studies of multi-quark potentials in lattice QCD to clarify the inter-quark interaction in multiquark systems. We find that all the multi-quark p potentials are well described by the OGE Coulomb plus multi-Y-type linear potential, i.e., the multi-Y Ansatz. For multi-quark systems, we observe lattice QCD evidences of "flip-flop", i.e., flux-tube recombination. These lattice QCD studies give an important bridge between elementary particle physics and nuclear physics.