The papers in these Proceedings were presented at the Nineteenth ACM Conference on Economics and Computation (EC'18), held between June 18 and 22, 2018, at Cornell University in Ithaca, New York, USA. Since 1999 the ACM Special Interest Group on Electronic Commerce (SIGecom) has sponsored EC, the leading scientific conference on advances in theory, systems, and applications at the interface of economics and computation, including applications to electronic commerce. Each paper was reviewed by at least three program committee members and two senior program committee members on the basis of significance, scientific novelty, technical quality, readability, and relevance to the conference. Following the tradition of recent iterations of the conference, the authors were asked to align their submission with one or two of the tracks. The next table summarizes the number of submissions and the number of accepted papers for each possible combination of tracks Of the 70 accepted papers, 36 are published in these Proceedings. The remaining 34, at the authors' request, are included as abstracts with pointers to full working papers that the authors guarantee to be reliable for at least two years. This option accommodates the practices of fields outside of computer science in which conference publishing can preclude journal publishing. We expect that many of the papers in these Proceedings will appear at a later date in a more polished and complete form in scientific journals. Papers were presented in two parallel sessions. To emphasize commonalities among the problems studied at EC, and to encourage discussion at the conference, sessions were organized by topic rather than by focus area, and no indication of a paper's focus area(s) was given at the conference or appears in these proceedings.