Fungi Imperfecti which induce biodeterioration of art objects on paper can be divided into two groups: those which initiate degradation and those with adaptivity to definite substrates, such as cellulose. Surface damage, discoloration, and structural destruction of the paper, together with their causes, are discussed in detail. The text contains a brief mention of treatments for removal of fungal growth. Factors affecting environmental conditions such as moisture, temperature, pH level, nutrients, effects of oxygen and light, are mentioned.