This paper investigates the question – why the Grand Duchy of Lithuania at the peak of its power in the 15th century, failed to acquire Klaipeda, its natural gateway to the sea, whereas the young post World War I state of Lithuania, having lost its historic capital – Vilnius, managed to annex Klaipėda and its region (Memelland). Historic facts and events, as well as evaluations and conclusions presented by Lithuanian and foreign historians, are examined by invoking classic and Lithuanian geopolitical statements and insights. Expansion to the East, which was intrinsic to the Grand Duchy of Lithuania at this time, is analysed as a major cause of its inability to expand to the Baltic shore. Opportunities to capture Klaipėda presented by the Thirteen Year War between Poland and the Teutonic Order in the 1450-60’s are evaluated. The 1923 annexation of Klaipėda and its region by Lithuania is shown as the result of a favourable geopolitical situation.