DETERMINING THE MECHANICAL STRUCTURE OF THE INTERIOR OF THE EARTH IS A FUNDAMENTAL PROBLEM OF GEOPHYSICAL RESEARCH. THE STRUCTURE PROVIDES IMPORTANT INSIGHT INTO THE CHEMICAL COMPOSITION AND DYNAMICS OF THE EARTHS DEEP INTERIOR AS WELL AS BEING NECESSARY FOR UNDERSTANDING THE RESPONSE OF THE EARTH TO INTERNAL AND EXTERNAL FORCING. SEISMIC TOMOGRAPHY CAN PROVIDE GREAT INSIGHT INTO THIS STRUCTURE BUT THE SEISMOLOGICAL DATA CONVENTIONALLY USED FOR DERIVATIONS OF MANTLE TOMOGRAPHY BODY AND SURFACE WAVES ARE NOT IN THEMSELVES SENSITIVE TO DENSITY VARIATIONS. A GLOBAL DENSITY MODEL IS TYPICALLY OBTAINED THROUGH SCALING OF SHEAR OR COMPRESSIONAL WAVE SPEED VARIATIONS. A NUMBER OF STUDIES HOWEVER CONSISTENTLY SUGGEST THAT THE DENSITY VARIATION WITHIN THE MANTLE IS ANTI CORRELATED WITHSHEAR WAVE SPEED VARIATION ESPECIALLY IN THE LOWER MANTLE. WE HAVE DEVELOPED AN APPROACH CALLED TIDAL TOMOGRAPHY BY WHICH THE SOLID EARTH RESPONSES TO SEMIDIURNAL LUNI SOLAR TIDAL FORCINGS AS MEASURED BY SPACE GEODETIC AND OR SEISMIC TECHNIQUES CAN BE USED TO PROVIDE IMPORTANT AND NOVEL CONSTRAINTS ON THE LONG WAVELENGTH DENSITY AND ELASTIC STRUCTURE OF THE DEEP MANTLE AS WELL AS ANELASTICBEHAVIOR AT TIDAL FREQUENCIES. THE APPROACH EMPLOYS AND EXTENDS SEISMIC NORMAL MODE THEORY FOR COMPUTING THE SEMIDIURNAL AND LONG PERIOD BODY TIDE RESPONSE OF A 3 D ROTATING AND AN ELASTIC EARTH AND REVISES OUR EARLIER NUMERICAL FORMULATION OF THIS PROBLEM. WE WILL USE THIS THEORY TO ANALYZE DATA FROM THE GLOBAL NETWORK OF GLOBAL POSITIONING SYSTEM GPS SITES TO INFER DEEP MANTLE ELASTICAND DENSITY STRUCTURE. WE WILL ALSO EXAMINE THE SENSITIVITY OF THE INFERENCES TO ERRORS IN THE OCEAN TIDAL LOADING MODELS.