Generation of high-energy photons via collision of relativistic electron and laser beams is known as inverse Compton scatteringor laser Compton scattering. Compton sources, photon sources based on Compton scattering, have been developed in the worldto realize high-flux/high-brightness X-ray/gamma-ray sources and exploit applications with energy-tunable and narrow-bandwidthphoton beams from these sources. Recent progress of electron accelerator and laser technologies will open a new era in Comptonsources. An electron beam of small emittance and high-average current contributes to improving spectral brightness of Comptonscattered photons. Flux of generating photons is also increased by a high-power laser together with apparatus such as laserenhancement cavity. We overview the current status of Compton sources including an experiment carried out at the CompactERL, which is the first demonstration of Compton scattering by combination of an energy-recovery linac and a laser enhancementcavity.