In this chapter, we describe how blended multi-component absorption profiles can be modeled. Simple deblending that bypasses radiative transfer and atomic and gas physics can be performed using multi-component Gaussian fitting. We show how further sophistication can be added by tying doublets or multiplets and forcing Gaussian components to match known line spacings. To extract column densities and Doppler broadening parameters for each component, we use Voigt profile fitting. We begin with a general expression for a multi-component absorption profile for which each component has a unique column density and Doppler broadening parameter. We then discuss progressively more complex Voigt profile fitting, starting with multiple components for a single transition, then multiple components for a doublet (two transitions from a single ion), and then generalize to multi-component multi-transition multi-ion absorption systems. We also discuss methods for measuring the turbulent velocity component and approaches to multiphase decomposition for ions of different ionization levels. We conclude by discussing fitters and fitting philosophies. Optimized AOD column densities are also discussed.