One of the main goals in condensed matter is to understand the collective excitations that emerge from the interactions  between fundamental degrees of freedom of a system.  A case in point are Goldstone modes, gapless excitations that arise whenever a continuous symmetry is spontaneously broken.  In certain cases, symmetry breaking also gives rise to gapped modes, associated with fluctuations in the amplitude of the order parameter.  These modes are analogous to the Higgs particle in the Standard Model of particle physics.  In this talk, I will review the experimental evidence for amplitude modes in a number of condensed matter systems, including superconductors, superfluids, antiferromagnets, and possibly even solids.  I will also discuss some recent theoretical progress in the understanding of amplitude modes in low dimensional systems.