Cristina, sister of King Felipe VI, face two counts of tax fraud carrying a maximum prison sentence of eight years for allegedly failing to declare taxes on personal expenses paid by a company she owned with her husband, Inaki Urdangarin.
She is the first member of Spain's royal family to face criminal charges since the monarchy was restored in 1975.
Urdangarin is accused of using his former title of Duke of Palma to embezzle about 6 million euros (USD 6.5 million) in public contracts through the nonprofit Noos Institute he co-ran.