This package provides a class for typesetting publications of Association for Computing Machinery. Changes version 1.08 SIGPLAN reformatting (Matthew Fluet); bug fixes version 1.09 SIGPLAN: revert caption rules (Matthew Fluet) version 1.10 Bug fixes version 1.11 Customization of ACM theorem styles and proof environment (Matthew Fluet). version 1.12 Bug fixes and documentation updates. Footnotes rearranged. Option natbib is now mostly superfluous: the class makes a guess based on the format chosen. version 1.13 Formatting changes: headers, folios etc. Bibliography changes. version 1.14 Warn about undefined citation styles; move definitions of acmauthoryear and acmnumeric citation styles before use. version 1.15 New structured affiliation command. New commands for acknowledgements. version 1.16 Formatting changes for headers and footers. version 1.17 Formatting changes for margins and lists. Bug fixes. version 1.18 Natbib is now the default for all versions. A unified bib file is used for all styles. Better treatment of multiple affiliations. version 1.19 Include 'Abstract', 'Acknowledgements', and 'References' in PDF bookmarks. version 1.20 Bug fixes, documentation updates version 1.21 Bibliography changes: added arXiv, some cleanup version 1.22 Bibliography changes for Aptara backend; should be invisible for the users. version 1.23 Added PACM PL journal option. version 1.24 Added IMWUT journal option. version 1.25 Updated PACMPL journal option. version 1.26 Bug fixes version 1.27 Bug fixes version 1.28 Bug fixes: natbib=false now behaves correctly.