Reverse chemical genomic approach is expected to greatly expedite the discovery of new compounds, which modulate biological phenotypes in various ways. However, toward this end, various contents and platforms must be well prepared in the research community. In this regard, genome-wide preparation of clones for production of proteins in either a native or a fusion form, which are conventionally called ORFeome clones, would play a crucial role in realizing reverse chemical genomics as an approach of choice. In this chapter, currently available ORFeome cloning technologies are overviewed and a selection guideline for them is provided.