The majority of excitatory synaptic transmission in the mammalian brain is mediated by the activation of AMPA-type glutamate receptors (AMPARs) by the neurotransmitter glutamate. The number of AMPARs clustered at synapses as well as their functional properties dictates the strength and timing of synaptic transmission. Therefore, determining the factors that control the trafficking and gating of AMPARs is critical to understanding how neurons process and encode information. While it was recently discovered that AMPARs interact with a family of auxiliary subunits called transmembrane AMPAR regulatory proteins (TARPs) that control the trafficking and gating of AMPARs, functional diversity among TARP family members has not been explored. In this thesis, I establish cultured cerebellar granule neurons from stargazer mutant mice as a model system to separately determine the effects of each TARP subtype on synaptic AMPAR function. I demonstrate that transfection of any of the TARP subtypes g-2, g-3, g-4, or g-8 into stargazer granule cells "rescues" the synaptic expression of native AMPARs, allowing an assessment of the roles of each TARP subtype in controlling synaptic AMPAR trafficking and gating (Chapters 1 and 2). I also employ TARP domain truncation and transplantation to determine which domains within TARP proteins mediate their subtype-specific effects on AMPAR trafficking and gating (Chapters 1 and 2). Finally, I exploit changes in the pharmacology of AMPARs induced by TARP binding to determine the stoichiometry of the association between TARPs and AMPARs (Chapter 3) and to infer structural information about which specific conformations of AMPARs are selectively stabilized by TARPs during gating (Chapters 4 and 5).