GIANT PLANET FORMATION LEADS TO TWO DISTINCT CLASSES OF PLANETS: GAS GIANTS LIKE JUPITER WHOSE MASS IS DOMINATED BY THEIR GASEOUS ENVELOPE AND SOLAR SYSTEM ICE GIANTS OR EXTRASOLAR MINI-NEPTUNES WHICH HAVE A SMALLER BUT STILL SUBSTANTIAL ENVELOPE. A CENTRAL RESULT OF THE KEPLER MISSION HAS BEEN THE OBSERVATIONAL DEMONSTRATION THAT PLANETS IN THE MINI-NEPTUNE CLASS ARE EXTRAORDINARILY ABUNDANT BUT THE PHYSICAL PROCESSES THAT DETERMINE WHERE SUCH PLANETS CAN FORM AND WHY SOME FRACTION GROW FURTHER TO BECOME GAS GIANTS REMAIN UNCLEAR. RECENT THREE-DIMENSIONAL SIMULATIONS HAVE SHOWN THAT SPHERICALLY SYMMETRIC MODELS FOR ENVELOPE ACCRETION ARE INADEQUATE BECAUSE COMPLEX HYDRODYNAMIC FLOWS ALLOW GAS TO CIRCULATE BETWEEN THE PLANET AND THE SURROUNDING GAS DISK. THE GOAL OF THE PROPOSED NETWORK IS TO DEVELOP THREE-DIMENSIONAL MODELS OF PLANETARY ENVELOPE ACCRETION THAT SELF-CONSISTENTLY INCLUDE THE PHYSICAL PROCESSES KNOWN TO INFLUENCE THE GROWTH OF GIANT PLANETS. BUILDING ON THE OPEN SOURCE ATHENA++ FRAMEWORK WE WILL DEVELOP SIMULATIONS THAT INCLUDE THE SELF-GRAVITY OF THE GROWING PLANET RADIATIVE TRANSPORT IN BOTH THE HIGHLY OPTICALLY THICK INTERIOR OF THE PLANET AND IN THE MODERATELY OPTICALLY THICK INTERFACE ZONE WITH THE DISK AND GRAIN OPACITIES THAT ARE COUPLED TO THE FLOW OF SOLID PARTICLES INTO THE ENVELOPE. THE NETWORK NODES WILL BRING COMPLEMENTARY EXPERTISE IN CODE DEVELOPMENT PLANET-DISK INTERACTIONS PLANETARY ENVELOPE PHYSICS AND PARTICLE TRANSPORT IN PROTOPLANETARY DISKS. THE SUCCESSFUL COMPLETION OF THE PROJECT WILL ADVANCE THE STATE-OF-THE-ART IN GIANT PLANET FORMATION FROM ONE TO THREE SPATIAL DIMENSIONS AND PROVIDE A FOUNDATION FOR UNDERSTANDING HOW THE GIANT PLANET DICHOTOMY IS ESTABLISHED AND WHERE AND WHEN THE GAS GIANTS AND MINI-NEPTUNES DISCOVERED BY KEPLER FORMED.