A magnesium halide composition comprising and/or made from a magnesium halide, a solvent suitable for an electron donor compound and an electron donor compound. The composition is characterized by enhanced solubility whereby it has a solubility in the solvent that does not decrease as a function of temperature up to the boiling point of the solvent and the solubility of the magnesium halide in the solvent is greater than 0.7 mol/liter. A polymerization catalyst precursor composition can be made from magnesium halide composition by mixing the magnesium halide composition with a transition metal compound.