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We report the discovery of 43 beat Cepheids in the Large Magellanic Cloud (LMC) using the MACHO Project photometry database. The variables which are pulsating simultaneously in two radial modes are shown to break cleanly into two period-ratio groups, providing the first unambiguous evidence that the second overtone is indeed excited in real Cepheids. Twenty-nine stars are beating in the fundamental and first overtone mode (F/1H, with a period ratio in the neighborhood of 0.72), and fourteen stars are beating in the first and second overtone (1H/2H, with a period ratio near 0.80). The F/1H period ratios are systematically higher than known Galactic beat Cepheids, indicating a metallicity dependence whose sense is in agreement with theory. Beat Cepheids in the LMC are found to select the 1H/2H mode for fundamental periods shorter than 1.25 days. We fail to confirm any of the proposed beat Cepheid candidates common to our sample and the surveys of Andreasen (1987) and Andreasen \& Petersen (1987).
