CGIwithR is a package for use with the R statistical computing environment, to facilitate processing of information from web-based forms, and reporting of results in the Hypertext Markup Language (HTML), through the Common Gateway Interface (CGI). CGIwithR permits the straightforward use of R as a CGI scripting language. This paper serves as an extended user manual for CGIwithR, supplementary to the R help pages installed with the package.