Some 60 addition compounds of the type MgCl2 . nEtOH (6 less than or equal to n less than or equal to 1.4), formed between magnesium chloride and ethanol, have been prepared and were characterized by means of X-ray powder diffraction. The spectra were interpreted on the basis of a subset of nine characteristic diffraction patterns, and a range of (partially) new products, MgCl2 . nEtOH with n = 6, 4.5, 4, 3.33, 2.5, 1.67, 1.50 and 1.25, is described. MgCl2 adducts with alcohols can be converted to active olefin polymerization catalyst supports through the elimination of the alcohol molecules from the adducts by thermal desolvation.