The present invention provides methods for generating and identifying mutations in C elegans. Disclosed herein are methods for introducing DNA into the C elegans germline, methods for expressing DNA in the C elegans germline, and methods for generating C elegans mutants by using controlled mobilisation of endogenous and heterologous transposons. Also disclosed are a transgene construct for expression in C elegans and methods for inserting single copy DNA sequences in the C elegans germline, and engineering mutations into the C elegans genome.