The increasing worldwide demand for enhanced fuel economy and lower greenhouse gas emissionsin the automotive market has driven immense innovatio n in internal combustion engine (ICE) technology. One of the promising methods to address the inherent drawbacks of fixed compression ratio engines is the application of Variable Compression Ratio (VCR) technology in the form of Adaptive Compression Ratio (ACR) engines. This research work discusses the principles of designing, mechanism of working, advantages, and drawbacks of ACR engines in automotive engines. Through dynamic real-time adjusting of the compression ratio, ACR engines have the potential to fine- tune combustion for maximum efficiency at low- load cruising and increased power under high- load conditions, with the added safety against en gine knock. This paper explores different mechanical designs used to provide variable compression, examines the attendant improveme nts in fuel efficiency and performance, and critically assesses the design, control, cost, and reliability challenges. In addition, it discusses the existing deployment of ACR technology in the automotive sector and provides insights into its future prospect as a pivotal enabler of more efficient and sustainable vehicles.