[en] Immediately after the discovery of fission in 1939 by Hahn and Strassmann and Meitner and Frisch, the latter authors gave a qualitative explanation of the process using the picture of a charged liquid drop. Still in the same year, Bohr and Wheeler developed this picture into their classical theory, which remained the basis for the description of nuclear fission for many years to come. Today it is known that many of the finer details of the fission process cannot be understood without reference to the shell structure of the nucleus. It is the merit of V. M. Strutinsky to have shown a practical way to combine the knowledge about shell structure with the liquid drop model in his open-quotes macroscopic-microscopicclose quotes method and to point to the important effect of shell structure on what we call the open-quotes fission barrierclose quotes. This chapter will thus describe the fission barrier first within the liquid drop model (Section II) and then discuss shell corrections according to the Strutinsky procedure (Section III). Section IV will deal with the transmission through the fission barrier, including the most immediate effects of its double-humped shape. Some of the more detailed consequences of this structure, namely the existence of different classes of compound nuclear states, will be briefly addressed in Section V; however, more detailed discussion of their effect will be postponed to Chapter 4. Finally, Section VI will describe some basic methods of obtaining experimental information on the shape of the fission barrier. 61 refs., 11 figs., 1 tab