Frustration in systems shows many interesting equilibrium and dynamical properties [1-6]. In frustrated classical systems, there is no ground state where all the interactions are satisfied energetically. Because the ground states in regularly frustrated classical systems have many energetically unsatisfied interactions, there are many degenerated ground states and the residual entropy is larger than that of unfrustrated systems. Figure 10.1 shows the ground states of three Ising spins on antiferromagnetic triangle cluster. The closed and open circles in Fig. 10.1 denote up and down spins, respectively. The crosses in Fig. 10.1 represent energetically unsatisfied interactions.