FPGAs are reconfigurable ICs that allow hardware functionality to be defined or modified after manufacturing, offering a flexible canvas that can be programmed as different designs. eFPGAs, integrated within sstem-on chips (SoCs) or ASICs, extend this capability to specialized applications, enhancing computational efficiency and adaptability. This chapter explores their architecture, programming methodologies, and applications across diverse industries. Since its inception, reconfigurable logic has garnered substantial attention from the research community. Over the course of several decades, numerous reconfigurable technologies have emerged. We describe the historical landscape of FPGAs. Our focus is on the evolution of the reconfigurable fabric over time, along with architectural advancements. This chapter also offers a comprehensive overview of eFPGA.