This review discusses recent advancements in particle engineering via spray drying, focusing on the design and functionality of microparticles with nanoscale substructures. It provides concepts and theoretical frameworks for particle design calculations, reviews experimental research on parameters influencing particle formation, and presents a classification based on dimensionless numbers to estimate how excipient properties and process parameters affect particle morphology. The review discusses various pharmaceutical applications, including low density particles, composite particles, microencapsulation, and glass stabilization, emphasizing the underlying particle formation mechanisms and design concepts. The review highlights the shift from empirical formulation efforts to an engineering approach based on a better understanding of particle formation in spray drying. It discusses the role of particle engineering in drug delivery systems, particularly in pulmonary delivery, where microparticles are used for systemic delivery of proteins and peptides. The review also covers the terminology and theory of structured microparticles, including definitions of core, shell, coat, and cellular structures. The review discusses the importance of particle size in spray drying, noting that spray dried particles are typically spherical and their size can be described by geometric diameter. It also discusses the aerodynamic diameter, which is the diameter of a unit-density sphere that has the same settling velocity as the measured particle. The review provides equations for calculating particle size and discusses the factors influencing particle size, such as feed solution concentration and droplet diameter. The review discusses the distribution of components in spray dried particles, focusing on the mechanisms that determine the radial distribution of components during the drying process. It discusses the evaporation of a solution droplet in a spray dryer as a coupled heat and mass transport problem, and provides equations for describing the evaporation process. The review discusses the formation mechanisms of particles, including the effects of Peclet numbers on particle morphology. It discusses the formation of hollow particles, solid foam particles, and composite particles, and their applications in pharmaceutical delivery. The review also discusses the challenges in understanding and controlling particle formation, including the role of surface activity and the deformation of shells during drying. The review highlights the importance of particle engineering in pharmaceutical applications, including the design of low density particles, composite particles, microencapsulation, and glass stabilization. It discusses the use of spray drying in the production of these particles and their applications in pulmonary drug delivery, as well as in other areas such as vaccine development and immunotherapy. The review concludes with a discussion of the challenges in understanding and controlling particle formation, and the need for further research in this area.This review discusses recent advancements in particle engineering via spray drying, focusing on the design and functionality of microparticles with nanoscale substructures. It provides concepts and theoretical frameworks for particle design calculations, reviews experimental research on parameters influencing particle formation, and presents a classification based on dimensionless numbers to estimate how excipient properties and process parameters affect particle morphology. The review discusses various pharmaceutical applications, including low density particles, composite particles, microencapsulation, and glass stabilization, emphasizing the underlying particle formation mechanisms and design concepts. The review highlights the shift from empirical formulation efforts to an engineering approach based on a better understanding of particle formation in spray drying. It discusses the role of particle engineering in drug delivery systems, particularly in pulmonary delivery, where microparticles are used for systemic delivery of proteins and peptides. The review also covers the terminology and theory of structured microparticles, including definitions of core, shell, coat, and cellular structures. The review discusses the importance of particle size in spray drying, noting that spray dried particles are typically spherical and their size can be described by geometric diameter. It also discusses the aerodynamic diameter, which is the diameter of a unit-density sphere that has the same settling velocity as the measured particle. The review provides equations for calculating particle size and discusses the factors influencing particle size, such as feed solution concentration and droplet diameter. The review discusses the distribution of components in spray dried particles, focusing on the mechanisms that determine the radial distribution of components during the drying process. It discusses the evaporation of a solution droplet in a spray dryer as a coupled heat and mass transport problem, and provides equations for describing the evaporation process. The review discusses the formation mechanisms of particles, including the effects of Peclet numbers on particle morphology. It discusses the formation of hollow particles, solid foam particles, and composite particles, and their applications in pharmaceutical delivery. The review also discusses the challenges in understanding and controlling particle formation, including the role of surface activity and the deformation of shells during drying. The review highlights the importance of particle engineering in pharmaceutical applications, including the design of low density particles, composite particles, microencapsulation, and glass stabilization. It discusses the use of spray drying in the production of these particles and their applications in pulmonary drug delivery, as well as in other areas such as vaccine development and immunotherapy. The review concludes with a discussion of the challenges in understanding and controlling particle formation, and the need for further research in this area.