This chapter contains sections titled: 16.1 The Class BQP, 16.2 Equations, Solutions, and Complexity, 16.3 A Circuit Labeling Algorithm, 16.4 Sum-Over-Paths and Polynomial Roots, 16.5 The Additive Polynomial Simulation, 16.6 Bounding BQP, 16.7 Problems, 16.8 Summary and Notes