Atom interferometers are devices that manipulate quantum-mechanical matter waves in the same way that optical interferometers manipulate light waves. And just as a laser is a coherent light wave, a Bose-Einstein condensate can be thought of as a coherent matter wave. Extending this analogy, it can be hoped that Bose-Einstein condensation will permit great advances in atom interferometry just as the laser revolutionized optical interferometry. In order to be useful for precision measurements, however, experiments must exhibit long coherence times and/or large arm separations. This can be difficult, especially in the presence of a confining potential. We have succeeded in implementing a BEC interferometer that exhibits stable interference for wave packets separated by as much as 0.4 mm, and noisy interference for separations up to 1.7 mm. It is exciting to see quantum effects at work over such macroscopic distances. It also opens the door to a variety of precision measurements, which we are beginning to explore.