Given the scope of what may be found in nature as well as in laboratories there are relatively few problems [quantum Mechanics](Quantum%20Mechanics%20(index).md) that are [exactly solvable.](Analytically%20solvable%20systems%20in%20quantum%20mechanics) Many systems may be exactly solvable, however, solving them may require too much computation to be solvable in practice. Thus we have a variety of [approximation methods](Approximation%20methods%20in%20quantum%20mechanics.md) we can use. # Quantum perturbation theory # Semi-classical approximations # Adiabatic approximations [Adiabatic theorem](Adiabatic%20theorem) #QuantumMechanics/ApproximationMethods #QuantumMechanics/ApproximationMethods/QuantumPerturbationTheory