The ancient Thai books or <i>Samut Thai</i> are important handwritten manuscripts in Thailand which have been in use for a long time. They are made of locally hand-made paper and folded accordion-fashion into the desired size for the books. A number of them are illustrated manuscripts while others contain only text. In this paper the materials and techniques used in their production, as well as their properties and causes of deterioration are described. The results obtained show that moisture, insects, and fungi play the most important role in the deterioration. This paper also reviews conservation treatments and experiments on the effects of insecticides and fungicides on the growth of insects and fungi found on the books. The restoration techniques and materials used are also given. -- AATA