TeXsis is a TeX macro package which provides useful features for typesetting research papers and related documents. For example, it includes support specifically for: Automatic numbering of equations, figures, tables and references; Simplified control of type sizes, line spacing, footnotes, running headlines and footlines, and tables of contents, figures and tables; Specialized document formats for research papers, preprints and ``e-prints,'' conference proceedings, theses, books, referee reports, letters, and memoranda; Simplified means of constructing an index for a book or thesis; Easy to use double column formatting; Specialized environments for lists, theorems and proofs, centered or non-justified text, and listing computer code; Specialized macros for easily constructing ruled tables. TeXsis was originally developed for physicists, but others may also find it useful. It is completely compatible with Plain TeX. The authors are Eric Myers and Frank Paige.