Unknown and unrecognized for years, the smear layer has become a force to be reckoned with during the last couple of decades. Most dentists now know it exists but are often puzzled as to whether or not they should cope with it. The full significance of the smear layer has been slow to be perceived. Its increasing importance has paralleled the interest in adhesive bonding to tooth structure. Undoubtedly, little attention would have been paid to the smear layer without interest in adhesive techniques. However, the total understanding of the significance of the smear layer is far from complete and whether it should be removed or not still remains controversial. But a total awareness of both the sides of a controversy will enable the clinician to find a way through the confusion. Hence this monograph is a humble attempt to review the morphology and physiology of the smear layer, its significance in Restorative Dentistry and Endodontics and the pros and cons of its removal or its retention. It will also entail to clarify and give a birds’ eye view of this enigmatic layer that is still wrapped in unresolved controversies, which may help answer some of the perplexing questions.