This volume, sixth in a series of collected works by world-renowned computer scientist Donald E. Knuth, assembles approximately two doxen of his pioneering contributions to the field of computer languages, including papers on ALGOL, SOL, RUNCIBLE, and FORTRAN. Papers on the early development of programming languages, the history of writing compilers, the characterization of parenthesis languages, and the semantics of context-free languages are also included.