The different performance and other general properties of the three major classes of finely divided synthetic amorphous silicas - precipitated silicas, silica gels and pyrogenic silicas - have their origin in inherent differences in their morphological characteristics, surface chemistry and purity levels. Even in the technical scientific literature, these concepts are not always clearly defined and understood, and mix-ups in industrial terminology add to potential confusion. The present article endeavors to improve this situation with an in-depth review of pertinent manufacturing processes, inherent product properties and performance parameters.