Being amongst the most versatile molecules available to promote adhesion, organosilanes nonetheless remain a bit of a conundrum for some as one needs to know their chemistry thoroughly in order to utilize them in a useful fashion. In the first instance, this work starts with a short presentation of organosilanes defining this class of chemicals as well as explaining their genesis followed immediately by a section of this chapter dedicated to their chemistry which includes a few words of warning. Closely related are the necessary interactions that such molecules have to develop on materials in order to fulfill their main role as adhesion promoters, and this is described too but more particularly when considering metallic substrates and polymers. Reactions in a medium are also covered briefly as silanes are commonly included in a matrix which precludes a more comprehensive section of silanes behavior in formulations later on in this document. Is also covered other usages of silanes than as adhesion promoters together with principles to follow in order to chose a silane for a particular application. The following section is concerned with the use of silanes as primers particularly where the user aims to improve adhesion or protect from corrosion. To complete this work, a small section covers some other organic or nonorganic adhesion promoters.