Helioseismology seeks to infer the properties of the solar interior using measurements of the global normal mode oscillations as a function of spherical harmonic degree l, azimuthal order m, and radial order n as observed on the solar surface. The frequencies, v
0(l, m, n), of the modes are influenced by the physical conditions of the solar plasma through which the p-mode (pressure) waves propagate, while the power, P(l, m, n), and line widths, Γ(l, m, n), provide clues about the excitation and damping of the oscillations. These mode parameters are extracted from observations of the solar surface using a long and complex data reduction procedure. It is thus important to precisely describe the steps in the reduction and to assess the influence of the choices on the resulting inferred physical conditions.