Transiting extrasolar planets are corner stones for the understanding of planetary systems. The transiting configuration, paired with precise photometric measurements of the system's flux across time, allow the measurement of fundamental planetary and stellar properties, as well as insights on the planet's atmospheric composition and thermal structure. This thesis describes the application of high precision photometry to the discovery and the atmospheric study of extrasolar planets. A detailed description is given of the installation, characterization and operation of EulerCam, a specialized instrument at the Euler-Swiss telescope. A major contribution has been made with EulerCam to the Wide Angle Search for Planets, where EulerCam has aided in the identification of planet candidates as well as provided a precise characterization of many newly-found planets. The atmospheric studies undertaken over the course of this thesis cover near-infrared measurements of emission from WASP-19b using both, EulerCam and the VLT/HAWK-I instrument, as well as measurements of the transmission spectrum of WASP-49b obtained from multi-object spectroscopy using the VLT/FORS2 facility.