While carboxylic acids are not the most reactive they are central in the reactivity of carboxylic acid derivatives.  The can be converted to any of the carboxylic acid derivatives.  Since the -OH of carboxylic acids is not the greatest leaving group a common theme is to convert it to a more reactive leaving group.  In general the more reactive acid chlorides and anhydrides are easily converted to alcohols (alcoholysis) and amides (aminolysis).