King Felipe's 50-year-old sister is one of 18 people on trial after a six-year investigation into the Noos Foundation, a charity run by her husband, Inaki Urdangarin, that prosecutors say was used to embezzle millions of euros in public funds.
Details of the investigation into the royal family emerged during the economic crisis when Spain was grappling with record unemployment and austerity and tapped into popular disgust at cases of high-level corruption among bankers and politicians.
Urdangarin, a former Olympic handball player who appeared alongside his wife in the Mallorcan court, is accused of using his royal connections to win public contracts to put on events through the non-profit organisation.
Prosecutors say some of the foundation's money was transferred to a company largely owned by the princess and Urdangarin and used to pay for personal items ranging from parking tickets to children's birthday parties.
Cristina is charged with two counts of being an accessory to tax fraud and, if found guilty, could face up to four years in prison. Urdangarin is charged with crimes including fraud and tax evasion with a potential jail sentence of up to 19 years.
The couple, who have four children, have denied any wrongdoing.
The popularity of Spain's royal family has revived since former king Juan Carlos abdicated in 2014 in favour of his 47-year-old son Felipe and former television journalist wife. The new king regularly tops popularity polls of public figures.
Felipe was proclaimed king in a low-key ceremony in 2014 and has since worked to modernise the monarchy, paring down the royal family's formal members and taking duties away from his two sisters.
He stripped Cristina of her title of Duchess of Palma in June.