We have discussed the impact of formulation composition, e.g., excipients, buffer, and sugar, in protein stabilization in the solid state. The freeze-drying process itself can also play an important role in determining the stability and critical attributes of the final product. The rate of cooling during the freezing process determines the degree of supercooling, morphology, porosity, and surface area of solid cake, which subsequently affects the rate of primary drying and stability of protein. If high supercooling is generated, smaller nuclei would form, and the crystal growth is limited which in turn results in small pores and high surface area. This can lead to more resistance in heat transfer with a longer duration of primary drying to remove the water and higher interfacial stress. However, the process of ice nucleation using conventional lyophilization is stochastic and heterogeneous. The ice can nucleate at different times/temperatures, or be triggered by impurities, which result in variability in crystal morphology, freezing time, and stability. Strategies to control ice nucleation can enable spontaneous and simultaneous nucleation to facilitate both the freezing and drying processes. Iyer et al. demonstrated that controlled nucleation could help maintain the native structure of proteins. Myoglobin structure with or without controlled nucleation was characterized by solid-state photolytic labeling mass spectrometry (ssPL-MS). Myoglobin lyophilized with controlled nucleation in the presence of sucrose showed greater pLeu incorporation and the fraction of intact protein labeled increased dramatically than for other conditions, suggesting greater protein-matrix interactions and enhanced stability. Similarly, Rui et al. found aggregation of human IgG and recombinant human serum albumin can be minimized with higher ice nucleation temperature (-5 vs. -12°C) which results in large ice crystals and limits the ice-water interface stress-induced protein adsorption and unfold. 262 6. Understanding stabilizing and destabilizing interactions in new and evolving modalities and delivery of peptide and mAb Drugs 6.1 Peptide stability