In Spain (last I checked we're in Europe) the most usual are two weeks by default. Contracts can extend it or you can leave at once while in the "test period",

In Spain (last I checked we're in Europe) the most usual are two weeks by default. Contracts can extend it or you can leave at once while in the "test period", fair because during this period the employer can fire you at once too without cause. You can leave immediately even subjected to this clauses, but then you suffer a penalization (one day of pay each two days you cut). Most times, the company owes you money at any given time (holidays, extra pays), so it's wise to stay unless the new salary nulls the difference. Also it's always good to keep good will with former employers, you never know.