Natively unfolded or intrinsically disordered proteins (IDPs) challenge the traditional sequence-structure-function paradigm and constitute one of the major classes of molecular workhorses. Unlike the folded (globular) proteins, IDPs lack the ability to undergo autonomous folding, exist as dynamic ensembles, and underscore the importance of conformational plasticity and heterogeneity in the protein function. However, the disorder-to-function relationships are poorly understood. Additionally, the dysfunction of many IDPs is associated with a range of deadly diseases such as Alzheimer's and Parkinson's diseases and cancers. My laboratory has been investigating the structural and dynamical characteristics of a wide range of disease-associated IDPs that undergo liquid-liquid phase separation and amyloid aggregation. I will describe our recent results that shed light on the intriguing conformational characteristics and unusual phase behavior of IDPs that undergo liquid-liquid phase separation leading to the formation of liquid droplets that can eventually undergo liquid-to-solid phase transition into more ordered aggregates. We utilized a wide range of multidisciplinary tools including time-resolved and single-molecule fluorescence spectroscopy to study the fundamental physicochemical factors that govern the conformational heterogeneity, distribution, and dynamics of IDPs involved in phase separation and aggregation. This lecture in the Department of Chemistry at IIT Bombay will aim at connecting the physical chemistry of IDPs to a broader biological context and will set the stage for my second lecture in the Department of Biosciences and Bioengineering at IIT Bombay.