The field of organic electronics has been heavily impacted by the discovery and development of π-conjugated conducting polymers. These polymers show great potential for integration into future optical and electronic devices due to their capacity to transition between semiconducting and conducting states as well as the ability to alter mechanical properties by controlled doping, chemical modification, and stacking or creating composites with other materials. Among π-conjugated polymers, polythiophene and its derivatives has been one of the most extensively studied and is widely investigated computationally and experimentally for use in electronic devices such as light-emitting diodes, water purification devices, hydrogen storage, and biosensors. Various theoretical modeling studies of polythiophene ranging from an oligothiophene approach to infinite chain lengths (periodic boundary conditions) have been undertaken to study a variety of electronic and structural properties of these polymers. In this review, we discuss the recent advances in the understanding of pristine polythiophene and its derivatives from fundamental perspectives to device applications.