When an exoplanet passes behind its host star, we can measure the time of the occultation, its depth, and its color. In this chapter we describe 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. This technique became a reality in 2005; in this chapter we describe the basics of the technique, its main results in the last 12 years, and the prospects for the years to come. This chapter includes a Table with references to all published detections of secondary eclipses until December 2017.