Expedition is a long journey in which groups of researchers are separated from the rest of the world, so they can discover new unexplored areas of the world. This thesis deals with research expeditions. The most significant Croatian researchers are emphasized in this paper. Mirko and Stjepan Seljan are more prominent researchers who performed expeditions in Ethiopia and South America where Mirko Seljan dies. They also had founded the Seljanville in Ethiopia, located between Rudolf's and Victoria's lakes. Dragutin Lerman is the second most significant researcher in this thesis that has come to Congo several times to study the lives of the natives. The last researcher mentioned in this thesis is Ferdinand Konšćak who, on three occasions, proved that California is a peninsula and he was also searching for sources of drinking water during of his three expeditions to California.