In silica-filled tire tread compounds, bi-functional silanes are essential to achieve the desired compound properties. The silane creates a covalent linkage between the filler and the polymer. Part 1 of this review paper describes the silanization reaction carried out in the mixer with the view of a chemist. Parameters to guarantee an efficient silanization reaction and to prevent an unwanted pre-scorch reaction are described. It becomes apparent that the optimal processing is always a compromise between temperature, mixing cycles and time, as well as the right choice and addition frequencies of the ingredients. In part 2, the paper reviews the silane development starting with the well-known tetrasulfide silane Si 69 (TESPT) to the latest generation of a highly efficient mercaptosilane derivate, Si 363.