People have always had a close relationship with the aquatic environment. This relationship includes the use of the sea for fishing and communication purposes. Nowadays, the sea is an important element of the transportation system, as it carries large volumes of cargo and passengers. In this chapter, we will provide a brief introduction to ships and shipping, focusing mainly on commercial vessels. However, many of the elements discussed in this book, such as emissions of exhaust gases, their effects, and preventive measures, are also encountered in other areas of shipping, such as recreational, research, and fishing vessels. This chapter also introduces the environmental impact of ship operations. The use of ships as a means of transportation has dramatically increased since the industrial revolution, resulting in increased emissions of exhaust gases and pressures on the environment.