Two novel processes for the carboxymethylation of starch are presented, and are compared with respect to degree of substitution, substitution patterns, reaction times and yield. The first process is a gel process in a continuous static mixer reactor optimised for handling concentrated aqueous starch pastes. The second process is a slurry process which uses organic liquids as reaction medium. Based on experimental results for both processes it can be concluded that each process has its own characteristic advantages. The static mixer process gives a good selectivity, it has short residence times and superior controllability and safety. Benefits of the non-aqueous slurry process are the possibility to produce granular CMS with a high degree of substitution and a good selectivity.