Intrinsically disordered proteins (IDPs) are a class of proteins that do not fold into a specific three-dimensional structure, which is a characteristic of proteins. The structural flexibility of IDPs range from fully structured to partially structured, which enables them to complement ordered proteins in order to perform functions that cannot be performed by rigid structures. Several factors such as pH and temperature can affect the shape and level of disorder in proteins. IDPs have been associated with various diseases such as cancer and cardiovascular diseases. The accumulation of an IDP called α-synuclein plays a pathophysiological role in Parkinson's disease (PD). The structural flexibility of the unstructured α-synuclein protein and associated disease mechanisms is affected by several factors such as genetics, oxidative stress, nitrative stress, and mitochondrial impairment. The book aims to shed light on some of the unexplored aspects of intrinsically disordered proteins and the recent researches on them. It will serve as a valuable source of reference for the graduate and postgraduate students.