This manual is the first volume of the reference documentation for R, a powerful free environment for statistical computing and graphics. The main commands of the base package of R are described in this volume. A second companion volume "The R Reference Manual - Base Package - Volume 2" (ISBN 0-9546120-1-9) covers the R commands for graphics, mathematical functions, distributions, models, time-series and sample datasets. Together the first and second volumes document the complete base package of R. Further volumes describe additional standard packages that can be used with R. All the reference manuals are written by the developers of R, and represent the definitive guide to the software. The manuals explain the use of each command in detail, with references, implementation notes and examples. Every volume includes a comprehensive index of entries listed by keyword and topic. The tutorial manual "An Introduction to R" (ISBN 0-9541617-4-2) provides introductory material for those learning to use R. R is free software, distributed under the GNU General Public License (GPL). It is available for GNU (GNU/Linux), Unix, Macintosh and Windows systems. For each set of manuals sold (volumes 1 & 2) $10 will be donated to the R Foundation to support the development of the software.