This chapter offers a complete assessment of the key role played by formulation additives in the development of pharmaceutical dosage forms. Beginning with an insightful introduction to formulation additives, the chapter emphasises on their significance in achieving desired product characteristics. A systematic breakdown follows, categorising formulation additives based on the types of dosage forms and providing detailed insights into the additives used in each category, shedding light on their functions and applications. The importance of understanding drug-additive interactions during formulation development has also been discussed, covering physical, chemical and therapeutic incompatibilities, along with analytical techniques to characterise such interactions. Recent advances in additive science, such as functional and co-processed additives and novel materials, are also explored along with international patented excipients. Additionally, the chapter provides insights into related regulatory perspectives, including generally recognised as safe (GRAS), international impurity guidelines (IIG) and International Pharmaceutical Excipients Council (IPEC), to ensure compliance and safety in pharmaceutical formulations. This chapter serves as a necessary source for those engaged in pharmaceutical product development, providing a comprehensive and up-to-date perspective on formulation additives.