The state and dynamics of the earth's ionosphere is completely controlled by the solar radiations. The amount of solar radiation incident on the ionosphere varies considerably with the solar activity, so does the ionospheric variability. In this book we investigate the influences of different Space Weather events like Solar Flares, Geomagnetic Storms and Solar Eclipse on the ionospheric variability. This book contains three chapters : Chapter 1 entitled "Investigation of Solar Flare Effects on GPS TEC and their positional dependence at Low, Mid and High Latitudes", Chapter 2 entitled "Performance evaluation of GPS under disturbed geomagnetic conditions" and Chapter 3 entitled "Ionospheric Effects of Total Solar Eclipse on 22 July, 2009 Observed Over Crest of EIA, Bhopal".The objectives proposed for the book have been achieved successfully in evaluating the effects of various type of Space Weather events on the ionosphere. The work contained in the book will help in designing the GPS receivers that will be capable of operating under adverse Space Weather conditions. This will help to improve the reliability and accuracy of GPS measurements in future.