Abstract: The aim of the paper is to characterise the acoustic conditions in the Baltic Sea, pointing their specific features and showing their impact on short and long term prognosis for the sound propagation. The paper contains the results of experimental and theoretical research based on a large number of in situ measurements. The acoustical climate of the Baltic Sea is difficult to characterise because of many factors influencing it. Seasonal changes in vertical sound speed distribution, typical for upper layer in shallow water, are the main factor influencing the wave propagation. But the difficulties in specifying the acoustical conditions are augmented by the appearance of anomalies as well as short term.