Now, given the considerations of background, peak shape functions, integrated intensity, and non-linear least squares minimization, the parameters used in the Rietveld refinement which put these things together can be introduced. Below are the groups of independent least squares parameters generally refined in a Rietveld refinement.
* Background parameters: usually 1 to 12 parameters.
* Sample displacement: sample transparency, and zero shift corrections. (move peak position)
* Multiple peak shape parameters.
** FWHM parameters: i.e. Caglioti parameters (see section 3.1.2)
** Asymmetry parameters (FCJ parameters)
* Unit cell dimensions
** one to six parameters (a, b, c, α, β, γ), depending on the crystal family/system, for each present phase.
* Preferred orientation, and sometimes absorption, porosity, and extinction coefficients, which can be independent for each phase.
* Scale factors (for each phase)
* Positional parameters of all independent atoms in the crystal model (generally 0 to 3 per atom).
* Population parameters
** Occupation of site positions by atoms.
* Atomic displacement parameters
** Isotropic and anisotropic (temperature) parameters.
Each Rietveld refinement is unique and there is no prescribed sequence of parameters to include in a refinement. It is up to the user to determine and find the best sequence of parameters for refinement. It is worth noting that it is rarely possible to refine all relevant variables simultaneously from the beginning of a refinement, nor near the end since the least squares fitting will be destabilized or lead to a false minimum. It is important for the user to determine a stopping point for a given refinement. Given the complexity of Rietveld refinement it is important to have a clear grasp of the system being studied (sample, and instrumentation) to ensure that results are accurate, realistic, and meaningful. High data quality, a large enough  range, and a good model – to serve as the initial approximation in the least squares fitting – are necessary for a successful, reliable, and meaningful Rietveld refinement.