Specific allergen immunotherapy has been practiced for allergic rhinoconjunctivitis for over 100 years and is the only treatment option that is disease modifying. In the USA, immunotherapy is usually administered via subcutaneous injection; this is the only route with a US FDA-approved formulation. There is growing interest in developing US-standardized formulations for the sublingual route, but up until recently there have been few US trials. Most of the experience with sublingual immunotherapy (SLIT) comes from Europe, where it is widely used and there is a large body of literature supporting its use. The purpose of this review is to summarize recent adult and pediatric clinical trials of SLIT in the USA. Most of the trials are for inhalant allergies, but there is some early work on SLIT as a novel therapy for food allergies.