When an exoplanet passes behind its host star, it is possible to measure the time, depth, and color of this occultation – or secondary eclipse. This chapter describes how these observables can be used to deduce physical characteristics of the planet such as its averaged dayside emission, departures from uniform disk illumination, or a precise measurement of the orbital eccentricity. The first secondary eclipses of exoplanets were detected in 2005; this chapter presents the basics of the technique, its main results in the last two decades, and the prospects for the years to come. This chapter includes a table with references to all published detections of secondary eclipses until January 2024.