With the completion of rice genome sequencing, the new challenge for the rice community is to unravel the biological functions of approximately 40,000 rice genes. To achieve this goal, a wide range of functional genomics tools, such as microarray, serial analysis of gene expression (SAGE), RNA interference (RNAi), insertional mutagenesis, and bioinformatics, have been established and employed. Insertional (T-DNA, transposon or retrotransposon) mutagenesis has proven to be one of the most efficient methodologies, because studies of mutants with detectable phenotypes have given us the greatest insight into the mechanisms underlying a wide range of biological processes in plants. Compared with T-DNA insertional mutagenesis, transposon insertional mutagenesis (or transposon tagging) has distinct advantages. Large-scale transposon mutagenized populations can be produced using a relatively small number of starter lines, as many independent insertions can be generated among the progeny of a single line. The tagged gene can be confirmed by revertants resulting from excision of the transposon. © 2007 Springer Science+Business Media, LLC. All rights reserved.