Library collections are often complex objects. Both of parchment manuscripts and leather artifacts are exposed to the fungal degradation due to unfavorable conditions. Controlling and avoiding fungal damage are considered one of the necessities that should be done by the conservators. A group of fungicides are used for this purpose. Antifungal agents with low toxicity and high efficacy are not used or even studied carefully; a new topic will be discussed in this book which has not been applied in the field of restoration and conservation of monuments before. The author study the effect of isolated fungi on the parchment manuscripts and leather artifacts; evaluate the efficiency of selected fungicides (in the form of chemicals components and essential oils) to control mycological degradation; follow the changes with ageing time in some properties of the parchment and leather and evaluate the appropriateness of these fungicides with the characteristics of parchment and leather and lack of impact on those properties. Finally, the author applied the Treatment and conservation procedures on the historical parchment and leather artifacts.