Esterification is the reaction of a carboxylic acid with an alcohol to form an ester and water.
The reaction is called a Fischer esterification.
Strong acid catalysts like sulfuric acid are needed.
A typical example is the esterification of acetic acid with ethanol to form ethyl acetate.
Esterification is an equilibrium reaction.
To drive the reaction to the right, the alcohol is often used both as the solvent and as the reactant, so it is present in large excess. Also, the water is usually removed as fast as it is formed.
Both conditions push the position of equilibrium to the right to give a maximum yield.
Saponification (Latin sapo = "soap" + facere = "to make") is the reaction of an ester with a base to form a carboxylate salt and water.
The name comes from the fact this reaction used to be used for making soap.
The reaction conditions are basic, so the product is a carboxylate ion rather than a carboxylic acid.
A typical example is the saponification of ethyl acetate.