"Damage does not always necessitate repair and old books don't always have to look as if they are brand new."
Dr. Nicholas Pickwoad, in B. Middleton, The Restoration of Leather Bindings, 4th edition, 2005; p. 277.

As applied to books, conservation treatment refers to "the intentional alternation of the chemical and/or physical aspects" of text and binding, aimed primarily at prolonging its existence.  In the definitions of the American Institute for Conservation (AIC), treatments may involve either stabilization or restoration, or both.  Stabilization includes procedures intended to maintain the integrity of the item and to minimize deterioration; restoration includes procedures intended to return an item to an earlier "known or assumed" condition, usually with the addition of non-original materials. 

In book conservation, "restoration" has in recent times not been a favored term. In large part this is due to earlier, inappropriate work carried out in attempts to "restore" early bindings. Even when done with great skill and finesse, as was often the case, such work seldom took notice of bibliographic evidence, and frequently emphasized ornament and appearance over function, structure or history. 

The preference now is for stabilization and "minimal intervention" rather than this earlier type of rebinding and restoration. But even within this limited scope there is a growing awareness that "almost all components of a binding have a story to tell," and that any intervention can result in the loss of historical evidence - even "as soon as the knife is inserted into a binding in order to initiate some repair . . ." (N. Pickwoad).

The value of "authenticity" in early bindings - even commercial bindings - can present collectors, curators and especially librarians with a dilemma.  Books are, after all, functioning structures and like all such structures they will eventually break down, for one reason or another. When access to the text is a primary concern - as it most often is in library collections - and the condition of an item threatens to restrict the appropriate level of access, then "restoring" or even replacing certain structural elements may become a necessity.  

Well planned conservation treatments seek to balance these contradictory demands. Decisions on how best to proceed in any given situation must be  informed by careful discussions with owners/curators and must be based on a thorough understanding of the nature and purpose of a particular collection.