The electroweak interactions are based on an extension of the electromagnetic (Maxwell) interactions, realized in a rather odd way so that the symmetries of the theory are not immediately obvious. This “broken” theory has been the subject of intense investigation at LEP, and has passed all tests with flying colors. These lectures are meant to complement the many excellent presentations of the StandardSU(2)L×U(1)Yelectroweak interactions in three main ways: first to clarify the physical meaning of symmetries in particle physics, second, to summarize the recent tests of the standard model using LEP data, and finally to look at possible roles of gravity in understanding mass. ©2001 American Institute of Physics.