Sublingual immunotherapy (SLIT) is available in two forms—either in a liquid preparation which contains allergen extract or in tablet form which dissolves when placed sublingually. Currently, only four sublingual tablet products are approved in the United States but there is “off-label” use of sublingual allergen extract drops practiced in the United States. In other parts of the world, including Europe, Australia, and Japan, there are many SLIT liquid allergen extract products. This section will further outline available products and the clinical evidence supporting these products.