Common experience teaches us that charges of like sign repel. Yet charged colloidal (mesoscopic-sized) particles in suspension can, under certain conditions, behave collectively as though mutually attractive. The most compelling evidence for attraction is the experimental observation of separation into concentrated and dilute phases, normally associated with pair attraction. In this talk, I will give a brief introduction to colloidal matter, review the basic forms of interaction between colloids, and finally discuss some remarkable implications for thermodynamic phase behavior.