The elemental composition of a multiphase material can be obtained by means of chemical and spectroscopic techniques. However, these techniques face a great difficulty in distinguishing the chemical identity of the phases present in the material and in derivation of the fractions of particular phases. X-ray powder diffraction seems to be an ideal technique for the analysis of a multiphase material. Each crystalline phase of the material gives its characteristic diffraction pattern independently of the other phases; this fact makes it possible to identify the phase of interest and to determine its fraction. The intensities of diffraction lines of a given phase are proportional to its fraction and an appropriate quantitative analysis can be performed after the application of the correction for the absorption of X-rays in the material. The principles of quantitative X-ray diffraction phase analysis of a multiphase material are presented, with a special attention paid to the doping methods. The following methods are described: (i) determination of the fraction of a phase using repeated dopings, (ii) determination of the fraction of a phase using a single doping, (iii) simultaneous determination of the fractions of several phases using a single doping; (iv) determination of the fraction of the dominant phase. The applicability of the doping methods is stated and the optimum conditions to minimize systematic errors are discussed. Recent approaches in quantitative X-ray diffraction phase analysis are also mentioned in short.