GCC nationals do not require an entry visa for Bahrain.
All other nationals residing in GCC who have a valid residence permit in their respective countries for at least 6 months will get an entry visa for Bahrain for one week on arrival at the Bahrain Airport or Causeway.
Nationals of some EU countries, Australia, Canada, Japan, New Zealand, Norway, Switzerland and USA may obtain visas on arrival for tourist or business stays of up to 2 weeks. If working for a media company (e.g. a newspaper or TV company) a special invitation from the Bahrain authorities is required.
Some Europeans, Americans, Malaysians by birth do not require a visa in advance. They will get a one-week visa at the Bahrain Airport immigration counter. Please check your eligibility here.