Karst soil is a result of destruction and dissolution of limestone rocks (calcium carbonate) in water rich with carbon-dioxide (CO2) and repeated sedimentation of dissolved material.
 45 % of surface of Croatia is karst soil. It spreads through Istria, Dalmatia, Dinaric and mountainous regions and Lika.
Chemical processes and tectonic changes turn sediment rocks- limestone, dolomites, salt and gypsum- into various underground and above ground karst forms.

Aboveground karst formations are sinkholes, karst valleys, karst bays and fields.
Sinkholes are furrow-like recesses and vertical cuttings in live stone. Sinkholes are the result of work of water on steep limestone blocks or crevices of flat rocks. Karst with that shape has very sharp edges and it is very rugged.
Karst valleys are funnel-shaped or disc-shaped recesses with stone or earth bottom. They were made following the dissolution of limestone and the underground sinking of surface water. Karst valleys are characteristic shapes for limestone, and they can range from 5 to 100 metres in diameter.
Karst bays can reach the length of up to several kilometres, and they are often the result of several karst valleys merging. Their bottoms are frequently fertile and farmed.
Karst fields are created by erosive work of rivers and sedimentation of deposits. Ličko polje and Krbavsko polje are the best-known karst fields in Croatia.

Corrosive influence of water underground produces numerous underground shapes such as caves, cavities, caves, caverns and other.
Pits are vertical or oblique openings of various depths. They are called abysses if the water sinks underground or goes out of them.
Caves reach out into the underground horizontally from their opening. They can be decorated with stalactites made by sedimented limestone from the ceiling and stalagmites when the limestone is sedimented from the floor.
Caverns are speleological constructions that are not connected with the surface by means of an opening, but they can nevertheless be quite large.

Croatian karst reveals more than 7000 caves, pits and abysses featuring a very large number of endemic and relict species of underground fauna. The largest number of caves is located on Velebit and Biokovo. According to the estimate, there are between 1000 to 2000 pits and caves in Istria.