Although entrance visas are obtainable at the airport for visitors arriving by airplane, those arriving by land must get a visa prior to arrival. These are obtainable from any Jordanian diplomatic mission abroad, where they generally take a day to be received. Visas cannot be obtained at Jordan's land border crossings.
Visas obtained in Jordanian consulates are valid for 3-4 months from the date of issue, and can be issued for multiple entries. Tourist visas allow a stay of up to one month initially. However, this period can easily be extended for up to another two months. After that date you must exit and re-enter the country, or undergo immigration procedures. If your visa has not been renewed properly by the time you leave Jordan you will have to pay a fine at the border. If you plan to stay for more than two weeks in Jordan, you will need to register at the nearest police station.