Built from a set of twenty standard amino acids, Proteins, the most abundant biological macromolecules found in living cells have great structural and functional diversity. Initially synthesized as linear polypeptide chains, they are required to fold to their unique native formats to gain function. Losing track during the folding process, proteins may misfold and end up as aggregates, causing neurodegenerative disorders. This book provides an overview of the protein folding scenario, the models and theories proposed, and consequences of misfolding have been discussed The book also provides a detailed in vitro study of the pH and solvent induced unfolding and aggregation of Hen Egg White Lysozyme. Evidence is presented for the presence of molten globule like intermediate at high pH and t-butanol induced amyloid like structure.