High-resolution maps of the temperature fluctuations in the cosmic microwave background radiation will provide valuable insight into the mechanism of structure formation in the early Universe. Theories involving Inflation generally predict a pattern of gaussian (random) noise, whereas theories based on symmetry breaking and the generation of defects-such as strings; textures and monopoles-have more distinctive signatures. Degree-scale measurements of the microwave background currently in progress should provide a powerful test of these competing theories.