The Solar TErrestrial RElations Observatory - STEREO, is a system of two identical spacecraft in Heliocentric Earth orbit. We use the two Heliospheric Imagers (HI) on board, which are wide angle imagers with multi-baffle systems to do high precision stellar photometry in order to search for exoplanetary transits and understand stellar variables. The cadence (40 min for HI-1 and 2 hrs for HI-2), high precision (< 1% scatter for R < 8 and a few per cent for fainter objects), wide magnitude range (R mag - 4 to 12) and broad sky coverage (nearly 20 percent just for HI-1A and 60 per cent of the sky in the zodiacal region for all the instruments combined) of this instrument marks this in a space left largely devoid by other current projects. This thesis describes the instrument and its capabilities, the semi-automated pipeline devised for the reduction of this data and the general characteristics of the data obtained. This thesis explains the data analysis methods used in identifying exoplanetary transits and stellar variables along with some of the early results. The thesis concludes with a description of the work in progress and also outlines some of the future prospects of this massive STRESS data set