Nine days after Juan Carlos called an end to a 39-year reign that guided Spain from dictatorship to democracy, parliament prepared for the future King Felipe VI to inherit the crown.
Prime Minister Mariano Rajoy opened the debate by defending the king and the monarchy, which he called "the best symbol of the unity of the state".
"Spain is a parliamentary monarchy with deep roots because Spaniards want it to be so," he added.
Once passed by the lower house, the succession will then have to be approved by the Senate, Spain's upper house of parliament, which will vote on the bill on June 17.
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The 46-year-old Prince Felipe is expected to be sworn in by parliament on June 19.
Anti-monarchist activists called for protests outside the building during the debate.
The succession must be enshrined in law under Spain's 1978 constitution.
But gaffes and a corruption scandal centred on his youngest daughter Cristina and her husband Inaki Urdangarin sent his popularity diving in the dying days of his reign.
His son Felipe, a former Olympic yachtsman married to glamorous former television news presenter Letizia with whom he has two daughters, eight-year-old Leonor and seven-year-old Sofia, commands greater popular support.