This article reviews recent advances in π-conjugated nanostructures based on conjugated oligomers and polymers, focusing on their preparation, energy transfer abilities, optoelectronic and laser applications, and photophysical properties including light harvesting. This is a rapidly evolving field as these materials are expected to have many important applications in areas such as light-emitting diodes, solid-state lighting, photovoltaics, solid-state lasers, biophotonics, sensing, imaging, photocatalysis, and photodynamic therapy. Other advantages of these materials are their versatility, and consequently, their adaptability to diverse fields.