This paper uses the failed AT&T/Time Warner merger as a case study to show that mergers between companies with markedly different cultures are likely to fail. Besides documenting the merged company’s worsening financial condition, the paper contrasts AT&T’s performance after the merger with similar mergers to highlight the importance of complementary cultures for the success of a similar merger. Though the problem of corporate chemistry is hard to measure, the investment community was a reliable guide for predicting its failure