As discussed in several chapters of this volume, frustration leads to unconventional (insulating) ground states. On the other hand doped holes are known to have profound effects in Mott insulators. Therefore doped frustrated systems offer the prospect of novel phases with some of the most fascinating, challenging and exotic behaviour. In addition, at commensurate electron fillings and in the presence of strong (screened) Coulomb repulsion, geometrical frustration can also manifests itself as an extensive degeneracy of the classical ground-state manifold providing profound similarities with the field of quantum frustrated magnetism.Magnetic frustration in quantum spin systems leads frequently to the formation of spin singlets (dimers). Generically, systems of fluctuating quantum dimers can often order, breaking lattice symmetries to give rise to Valence Bond Crystals (VBCs) [1], but under other circumstances they may remain in a quite unconventional quantum disordered state, the spin liquid, which breaks neither spin nor lattice symmetries. Anderson's original d-wave Resonating Valence Bond (RVB) state [2] is a paradigm for the spin liquid (in fact, for a particular type of gapless spin liquid, while the short-range RVB state composed of only nearest-neighbor dimers is gapped spin liquid). In a number of cases, frustrated spin systems and/or dimer systems can be doped, for example by chemical substitution in a Mott insulator. When both spin and charge degrees of freedom are present, the role of frustration becomes unclear, and to date remains only poorly explored. It is, however, clear that new and exotic phenomena emerge upon doping, including heavy-fermion behavior, spin-charge separation or quasiparticle fractionalization, unconventional superconductivity, stripe formation, bond and/or charge ordering, and many