Occultations for Probing Atmosphere and Climate: Setting the Scene -- 1. Occultation Methodology in General -- Wave Optics Algorithms for Processing Radio Occultation Data in the Lower Troposphere: A Review and Synthesis -- The Radio-Holography Approach for GNSS Occultation Data Analysis: Review and Application to Resolving Fine Structures in the Atmosphere and Mesosphere -- Open Loop Tracking and Inverting GPS Radio Occultation Signals: Simulation Study -- Fourier Analysis of GNSS-LEO Radio Occultation Signals, Resolution and Limitations -- Canonical Transform Methods for Radio Occultation Data -- Unfolding of Radio Occultation Multipath Behavior Using Phase Models -- Abel Integral Inversion in Occultation Measurements -- Does a Priori Information Improve Occultation Measurements? -- Retrieval of Atmospheric Refractivity Profiles from Ground-Based GPS Measurements -- 2. GNSS-LEO Occultation -- GRAS-SAF Radio Occultation Data from EPS/Metop -- Deviations from a Hydrostatic Atmosphere in Radio Occultation Data -- Sensitivity of GNSS Occultation Profiles to Horizontal Variability in the Troposphere: A Simulation Study -- Advancement of GNSS Radio Occultation Retrieval in the Upper Stratosphere -- Ensemble-Based Analysis of Errors in Atmospheric Profiles Retrieved from GNSS Occultation Data -- Refractivity Profiles Obtained by Abel Inversion from a Down Looking GPS Radio Occultation Experiment at Mt. Fuji: Preliminary Results and Future Plan -- 3. LEO-LEO Occultation -- An Active Microwave Limb Sounder for Profiling Water Vapor, Ozone, Temperature, Geopotential, Clouds, Isotopes and Stratospheric Winds -- An Overview of the University of Arizona ATOMS Project -- The ACE+ Mission: An Atmosphere and Climate Explorer Based on GPS, GALILEO, and LEO-LEO Radio Occultation -- Simulating the Influence of Horizontal Gradients on Retrieved Profiles from ATOMS Occultation Measurements - A Promising Approach for Data Assimilation -- Water Vapor Profiling Using Absorptive Occultation Measurements: A Comparison Between SAGE III and ATOMS -- The Genesis of the ACE+ Anti-Rotating Satellites Concept -- 4. Stellar and Solar Occultation -- The Stellar Occultation Technique: Past Achievements, Recent Developments, and Future Challenges -- Envisat/GOMOS Stellar Occultation: Inversion Schemes and First Analyses of Real Data -- Atmospheric Density, Pressure and Temperature Profile Reconstruction from Refractive Angle Measurements in Stellar Occultation -- Stratospheric Temperature and Ozone Sounding with ENVISAT/GOMOS Stellar Occultation -- Information Approach to Channel Selection for Stellar Occultation Measurements -- The Solar Occultation Mission ACE: An Overview -- Mesospheric Temperature and Ozone Sounding by the SMAS Solar Occultation Sensor -- 5. Use of Occultation Data -- Utility of Occultations for Atmospheric Wave Activity Studies: Results of GPS/MET Data Analyses and Future Plan -- Stratospheric Gravity Wave Fluctuations and Sporadic E at Mid-Latitudes with Focus on Possible Effects of the Andes -- The Detection of Upper Level Turbulence via GPS Occultation Methods -- Evaluation of Refractivity Profiles from CHAMP and SAC-C GPS Radio Occultation -- Ionospheric Radio Occultation Measurements and Space Weather -- The Mars Atmospheric Constellation Observatory (MACO) Concept -- Author Index.