Croatia is a member of the EU since the 1th of July 2013 and therefore there are no customs controls only police control for persons passing the Croatian border. So you will need to show your valid passport or identification card when from an EU country, if you’re from outside an EU country you have to show a valid passport. During summer months there can be long traffic lines for the border towards Istria and Zagreb especially on Fridays and Saturdays.

Here are the most used international border crossings as they are linked to the highways to and from Croatia

• Slovenia – Croatia
  highway A1/E61 Ljubljana to Koper – Porec, Pula A9/E751
  border crossing: Dragonja, Slovenia / Plovanija-Kastel, Istria, Croatia
  highway A1/E61 Ljubljana exit Postonja for Rijeka A7
  border crossing: Jesane, Slovenija / Pasjak-Rupa, Istria, Croatia
  highway A3 Ljubljana to Zagreb A3/E70
  border crossing: Bregana Slovenia-Croatia
  highway A2/E59 Maribor to Zagreb A1
  border crossing: Macelj Slovenia-Croatia
  Highway A5 Maribor to Cakovec D209, Varazdin
  border crossing: Lendava, Slovenia / Murska Sredisce, Croatia
• Hungary – Croatia
  highway M7/E71 Budapest/lake Balaton to Varazdin, Zagreb A4/E65
  border crossing: Letenye, Hungary / Gorican, Croatia
  highway M6/E73 Budapest – Osijek E73
  border crossing: Mohacs/Udvar, Hungary / Dubosevica, Croatia
• Bosnia and Herzegovina (BiH) – Croatia
  road A1/E73/M14.1 Sarajevo to Slavonski Brod, Zagreb, Croatia E70
  border crossing: Slavonski Brod
  road E661 Banja Luka to Zagreb A3/E70
  border crossing: Gradiska
  road A1/E73 Sarajevo-Mostar-Medugorje BiH to Ploce-Makarska, Croatia A1/E65
  border crossing: Bijaca, BiH, Nova sela, Croatia
• Neum corridor In Croatia at the height of peninsula Peljesac there is a small area (9 km) belonging to BiH, therefor you have to cross the border here before going to Dubrovnik! You do not need a visum if you just transit from Ploce Croatia to Dubrovnik Croatia. There can be some heavy traffic in summer months, but passing the border is usually without any problems.
  road M2/8 Ploce – Neum (BiH) – Dubrovnik
  border crossings: Klek and Neum/Kamenice (BiH), there are two lines one for passengers with destination BiH, and another for crossing/transit for Croatia
• Montenegro – Croatia
  road 8 Dubrovnik, Cavtat to Podgorica, Montenegro
  border crossing: Plocice
• Serbia – Croatia
  highway E70 Belgrado to Slavonski brod, Osijek E73
  border crossing: Batrovci, Serbia / Lipovac, Croatia