More than three-fourths of the 120-megabase Arabidopsis genome sequence has been determined, and the remainder will be released in the public sector within the next 1–2 years. This presentation will focus on two new technologies developed at the University of Wisconsin to facilitate a more rapid and complete understanding of the in situ function for the 25,000 proteins that are predicted to be encoded by the genome. The first technology is a large collection of T-DNA insertionally mutagenized mutant plants, and a means of scanning them in order to isolate several knockout alleles for each gene. By analyzing the phenotype caused by the absence of only one of the 25,000 genes, this reverse genetic approach provides a definitive means of determining the in situ function of all plant genes represented in the Arabidopsis genome. The second technology is a “maskless” microarray synthesizer, which allows one to perform combinatorial chemistry on a glass surface using light-sensitive reactants.