Cas9-triggered homologous recombination is a fast and inexpensive way to make essentially any desired change to the genome of C. elegans.   

We described this technique in detail in a publication (Dickinson et al. Nature Methods 2013).  We have created this web site as a genome engineering resource for the C. elegans research community. We'll keep it up to date with new protocols, reagent information and answers to questions. 
Best of luck with your experiments!

-Dan Dickinson and Bob Goldstein

New on 9/25/14:  Geraldine Seydoux's lab has just published a paper showing that 30-60 nucleotide homology arms can support efficient homologous recombination in C. elegans.  This is a major advance, because the homology arms can now be included in PCR primers — eliminating the need for cloning, which was previously the most labor-intensive part of our method.  
Stay tuned, we'll be updating the protocols on our website soon.