CONCERTO (CarbON CII line in post-rEionization and ReionizaTiOn) is a low-resolution spectrometer with an instantaneous field-of-view of 18.6, operating in the 130—310 GHz transparent atmospheric window. It is installed on the 12-meter Atacama Pathfinder Experiment (APEX) telescope at 5 100 m above sea level. The Fourier transform spectrometer (FTS) contains two focal planes hosting a total of 4 304 kinetic inductance detectors. The FTS interferometric pattern is recorded on the fly while continuously scanning the sky. One of the goals of CONCERTO is to characterize the large-scale structure of the Universe by observing the integrated emission from unresolved galaxies via the line intensity mapping technique. In this presentation, I will introduce the CONCERTO instrument and show some first results.