The Caspian Sea is situated on the border of Europe and Asia. It is bordered with the Russian Federation, Kazakhstan, Turkmenistan, Azerbaijan and Iran. The Caspian is the largest inland body of water in the world.

Since the ancient times, this water basin was in the focus of attention of famous travelers, scientists and state officials for its beauty, magic and enigmatic world.

Experts consider that during the Triassic period which covered 30 thousand years in the beginning of the Mesozoic era the land dominated the earth and seas appeared during to the flood. The sea which was called the Tetis in the scientific literature was surrounded from one side by Spain and from the other side it extended till the Zond islands. However, the sand and limestone sediments, accumulated through a long period of time promoted the formation of a land in late Mesozoic era that lasted for 70 million years in the Cretaceous period. The process did not stop at that stage and as a result the Caspian Sea gradually separated from the Black Sea. Yet the size of the lake either expanded or minimized at different periods of time. Researchers also called it the Aghzhaqyl sea which extended from Iran to the Kuybyshev city.

Though the Caspian Sea have passed different stages in its evolution, the sharp climatic changes (the icing up in Europe, Asia and North Armenica and the period of melting) caused constant changes in its area. It's possible to speak on different names of the Caspian Sea on the basis of the theories and thoughts of scientists and travelers, engaged in the exploration of the Caspian Sea. Some sources point out 40 names of the sea, others 100 of them. The said names were attaches to the sea depending on the countries, provinces and states which situated on the Caspian seashore and in these connection it is possible to point out such names as the Hirkan, Abeskun, Khazar, Khvalynsk, Kaspi, Pontik, Kimmerik, Sarmat, Khorasan, Tabasaran, Mazandaran, Goy, Aghdeniz, Rus, Baku, Derbend and other names. Among them only the Caspian sea and Khazar received the geographical and historical status and survived up to the present times.

The ancient Greek geographer and historian Hekatey Miletli (6-5th centuries B.C.) first spoke on the Caspian Sea and called it the oceanic basin or the Hirkan sea. Soviet historian L.A.Yelnski analyzed the geographical views of Hekatey and his contemporaries and came to a conclusion that the scientists of that period considered all seas, except for the Mediterranean Sea, to be closed. Yet the connection of the Red and Arabian Sea with ocean was discovered in the times of Herodotus. It's obvious that Herodotus spoke against the application of views on one of seas to others. Therefore, he pointed out that the Caspian Sea was not communicated with the ocean. It was proposed to attach the status of the lake to the Caspian Sea in the 5-6th centuries. At the same time, opposition theories also existed. Ptolemy who lived in the 2nd century B.C. also confirmed Herodotus's view. In the times when the commander Macedonian Alexander stayed at the banks of Syrdarya (at that time the Caspian and Azov Sea were not separated from each other) the allies of Alexander considered the Syrdarya to flow into the Caspian Sea and the Don river into the Sea of Azov and the Caspian Sea and the Azov Sea join each other. Great philosopher Aristotle also protected the idea of the Caspian Sea isolation. Yet it is not possible to say the reason he ruled out the Caspian Sea's underground communication with the Black Sea.

According to the information of Flavius Arrian who lived in the 4th century B.C. the Macedonian Alexander instructed Patrokka to investigate the matter of the Caspian Sea's communication with the north and east oceans to put an end to the conflict on the matter and later he entrusted it to Heraclites to establish a maritime fleet in the south for examination of the seashore. Yet the settlement of the matter was delayed to forty years. The task was fulfilled by one of Alexander's heir Selevk Nikator.

In 285-280 B.C. the Hirkan ruler ordered Partocle to travel all about the sea to study the nature of the Caspian Sea, that is whether it communicates with any other seas and with which of them it communicates. Partocle was the educated state official and scientist of that rime. Yet he drew out a very strange conclusion in his work devoted to his journey around the sea. The researcher Seyran Veliyev wrote that according to Patrocle the Caspian Sea is communicated with the north ocean. The researcher did not elaborate on the reason for such a conclusion due to the absence of the work. Yet the scientific literature contains quite opposite views. Some scientists consider that Patrocle regarded the road leading to the Garaboghaz-Gol gulf to be the strait to the north ocean, others explained the view with the fact that the peninsula that expanded till Mangyshlag turned to the north thus proposing the beginning of the ocean and some scientists write that Partocle took the Volga as a strait leading to the ocean.

L.A.Yelnsky analyzed these facts and pointed out that Patrocle sailed only till the Absheron peninsula of the Caspian Sea as he considered the other part of to be the North Sea. Thus, though ancient people considered the Caspian Sea to communicate with the ocean, Ptolemy stated the isolation of the Caspian Sea on the basis of old and new information in the 2nd century B.C. The victory of the view was possible only within a century after that. Later a number of scientists also considered the Caspian Sea to be part of the ocean. It should be mentioned that the lake nature of the Caspian Sea and its isolation from any ocean was confirmed only after a struggle which lasted for over 2 thousand years. It's not possible to compare the Caspian Sea with the Black, Baltic and other seas.

On the whole, the information about the Caspian Sea was mostly provided by Greek authors (Hekarey, Herodotus, Erotosfen, Strabon, Ptolemy and others), Arabian scientists, familiarized with the views of Greek authors (Yagut Hemevi, Zakariyye Gazvini, Abul Fida, Istekhri, Idrisi) and later, Persian, Turkish, European and Russia travelers (I.F.Seymanov, Q.V.Abikh, N.N.Andrusov and others). Masudi that lived in the 10th century provided information about Russia vessels sailing in the Caspian Sea and oil extracted in Baku. Arabian thinkers Istekhri and Idrisi pointed out the isolation of the Caspian Sea in the 900s B.S. Istekhri wrote: "It is possible to return to the initial position if one leaves from one point and moves along the coastline of the Caspian Sea".

The history of the Caspian oil states that Macedonian Alexander, initiating a war with Iran in 331 lightened the tent he lived in with oil burnt in the clayey dishes brought by the people living along the Caspian Sea shore. The Sea was called Khazar since the 15th century and its first map was drawn in 1616-1617. The wider exploration of the Caspian Sea was conducted by Russians by the instruction of Peter the Great in the 18th century, and a new map was drawn in 1717. The expedition of A.Berkovich-Cherkassky sailed to the eastern shore of the Caspian Sea and gathered information about it by the instruction of Peter the Great. I.F.Soymonov conducted the analysis of the Caspian Sea in the 1720s and a general map was drawn in 1731. I.V.Tokmachyov and M.I. Voynovich made a great contribution to the exploration of the Caspian Sea in the second half of the 19th century. Kolodkin for the first time worked out the compass picture of the Caspian coastline in early 19th century. This work was continued under the control of the counter-admiral I.Ivasintsev in mid 19th century. The work of the expedition lasted till 1856 and two volume atlas on the Astrakhan-Baku-Ashurada "the brief hydrographic description and the guidance to the sail in the Caspian Sea" was issued as a result of the expedition in 1874.

P.S.Kollas, K.M.Ber, Q.V.Abikh, E.X.Lents, N.I.Andrusov and others undertook steps to study the natural conditions of the Caspian Sea and the officials of the Baku customs office and the Caspian hydro-meteorological department made a great contribution to this process. An expedition led by I.M. Knipovich carried out various operations in the Caspian Sea in 1904-1912-1915. Beginning from the early 20th century soviet geologists I.M.Qubkin, B.A.Appolov, K.P.Voskresenski and Azerbaijani experts K.K.Gul, E.M. Shykhlinski, A.Q.Qasymov, M.I.Abakorov, A.I.Khalilov and other conducted valuable investigations concerning the Caspian Sea. Azerbaijani scientists mainly started the investigation of the Caspian Sea in 1947.

The Caspian Sea, which was of great economic and political importance became the object of Russia's interest sin the 18th century. Russia and Iran used the sea basin freely after the occupation of Azerbaijan in the 1830s. The geological history of the Caspian Sea, its oil and gas fields and biological conditions and other were studied by the Azerbaijani experts. This period is notable by wars between Russia and Iran on the control over the sea and a number of interesting points attract special attention.

The northeastern length of the Caspian Sea is approximately 1200 km, its average width is 320 km, the length of the coastline is 6.5 thousand km (including 800 km on the territory of Azerbaijan) and its area reaches 370 thousand km2 (it was 422 thousand km2 in 1929) and it lies 28 meters below sea level. The sea accounts for nearly 50 islands and 130 rivers that flow into it. Within the last 160 years the level of the Caspian Sea hesitated between 25.2 meters (1882) and 29 meters (1977) and the decline in its level amounted to 3.8 meters and 3.2 meters with the last 100 years. As a result of the rise in the water level of 1975-1995 an area of 12.5 thousand km2 of land was flooded. At that period the area of 48450 hectares was flooded and the damage of USD 2 billion was caused to Azerbaijan.

Considering the flooded Karvansaray island of the Baku bay and the remnants of forests flooded in Lenkoran it is possible to say that in the 12-13th centuries the level of the Caspian Sea was much lower than that of the present day. The Marino-Sanuto map found on the western coast of the Caspian Sea in 1320 reads: "The sea rose by several inches a year and flooded a number of good cities". As is seen, the Caspian Sea we are speaking about has a wide history. It informs us on the great importance that has been attached to the sea through centuries. Yet, the oil which played a great role in the industry attracted attention of the regional countries. Russia's struggle in the Caucasus mainly aimed to take the control over such large basin as the Caspian Sea. Therefore, the last 150 years in the history of the Caspian Sea are rich of interesting events. 432 million tons of oil and 318 billion m3 of gas were extracted and 26 large fields were discovered through the reported period.

Russia was a leading country in the assimilation of such a great volume of reserves. Oil was for the first time in the world produced from the wells drilled in the Caspian bay in 1798-1830. Beginning from 1872 the oil giants of Europe got interested in the Baku oil Robert Nobel (1829-1896) together with Brothers Ludwig and Alfred spent 25 thousand rubles for the development of the Absheron and Caspian fields and the construction of the oil plant. Those brothers created an oil company in 1879 and the first oil vessel in the world was commissioned by the order of L.Nobel in 1877. The largest tanker in the world "Zaratustra" operated for 40 years in the Caspian Sea. Rothschilds also expressed interest in the Caspian oil and they took the second place for their oil activity. The Caspian oil was processed under the protection of Moscow and the equipment used for this purpose was gradually improving in the Soviet times. The industrial production of oil commenced in the Caspian Sea in 1949.

The Caspian oil was the most important source of incomes of the Soviet Russia in the 1950s. Q.M.Gul, the prominent Azerbaijani geographer, dealing with the exploration of the Caspian Sea wrote in the 1970s: "The reserves of the Caspian Sea are variegated. The Caspian Sea may serve the universe and supply it with everything till there is a world. Therefore, it's necessary to define the ways of rational utilization of the Caspian Sea's natural resources through the economic potential."

Yet the socioeconomic processes that occurred in the 1990s created a new turning-point in the history of the Caspian Sea and as a result of that over 10 different contracts signed between the former USSR and Iran stayed in the shadow. The region is now composed of five independent states that included the theory of the new development of the Caspian Sea into their foreign policy, turning to the internationally important matter. Therefore, the socioeconomic processes of the present-day history of the Caspian Sea are as interesting as complicated.