The edict was signed at Granada in March 1492, weeks after the last Muslim kingdom in the peninsula had surrendered, and it gave the Jews of Castile and Aragon until the end of July to accept baptism or leave the kingdoms, taking their movable goods but not gold, silver or coin.
The stated reason was not that Jews were dangerous in themselves but that their presence drew converts back to Judaism. Spain had a very large population of conversos, families converted under pressure in the century before, whose sincerity was permanently suspect and whose supervision was the reason the Spanish Inquisition had been established in 1478. The expulsion was, in the logic of its authors, an attempt to complete a process rather than to begin one.
The numbers who left are disputed. Older estimates ran to hundreds of thousands; recent work on the documentary evidence has produced considerably lower figures, with a substantial proportion converting and remaining rather than departing. What is agreed is the destinations: North Africa, the Ottoman lands, Italy, and above all Portugal, which admitted them for a payment and then in 1497 forcibly baptised those who had come, closing the last nearby refuge and creating a second converso population under the same suspicion.