Publisher Summary This chapter discusses the sensitivity compensation and sensitivity synthesis. It presents a design procedure for achieving compensation to plant parameter variations because of external variables. It is based on an extension of the concept of sensitivity to that of dependency on several variables. This extended sensitivity concept is useful as a general analytical tool and is presented first in a general form. The methods described in the chapter could be used to achieve complete compensation if there was a way of synthesizing sensitivity functions independently of the transfer function. Such a synthesis is also of general interest and conceivable of having many applications. The problem has been shunned in the past because it has been known that the sensitivity function is tied to the system function and has as its poles the zeroes and poles of the system function. It seems there was no way to separate the critical frequencies of the sensitivity from these of the system function. It is found that one way in which these could be separated is to utilize surplus factors.