The use of modern high-precision solution calorimeters to study the association of amphiphiles in solution is discussed. Examples of studies made by the author and coworkers are given. The thermodynamic properties for micelle formation of poly (oxyethylene) alkyl ethers, C_nE_x, in water and formamide solutions are summarized. Studies of the association of sodium dodecylsulfate SDS in water and aqueous pentanol solutions made to test a thermodynamic model for the association of ionic amphiphiles are described.