The best possible allergen immunotherapy clinical outcomes require the provision of high quality and safe allergen immunotherapy extract preparations. Evolving national guidelines and regulatory bodies have devoted special attention to the safe compounding of sterile products, including allergen extracts. It is incumbent upon allergists preparing extract treatment sets for patients to be familiar with and adopt training, procedures and safety measures that lead to standardized high quality products. Preparers and supervisors must maintain ongoing competency in aseptic technique and prescribing principles, such as probable effective dose ranges, allergen cross-reactivity, and separation of high protease-containing extracts from susceptible extracts. Accordingly, knowledge and application of vial labeling, diluent selection, standard operating procedures, mixing log documentation, and mixing condition principles are a necessity. Although there have been no instances of infectious complications from allergen immunotherapy in a century of clinical practice, continued vigilance in the use of measures that ensure extract sterility is paramount. A review of allergen immunotherapy preparation recommendations and best practices based on published national guidelines is presented. Further study of preparation measures and prescribing principles will continue to advance the practice of allergen immunotherapy and offer opportunities for refinement of current recommendations.