The drive to more fuel efficient vehicles is underway, with passenger car targets of 54.5 mpg fleet average by 2025. Improving engine efficiency means reducing losses such as the heat lost in the exhaust gases. However, reducing exhaust temperature makes it harder for emissions control catalysts to function because they require elevated temperatures to be active. Addressing this conundrum was the focus of the work performed.The primary objective of this work was to identify low temperature limiters for a variety of catalyst aftertreatment types. The ultimate goal is to reduce catalyst light-off temperatures, and the knowledge needed is an understanding of what prevents a catalyst from lighting off, why, and how it may be mitigated. Collectively these are referred to here as low temperature limiters to catalyst activity. This paper describes the work performed to identify low temperature limiters to catalyst activity for gasoline Three Way Catalyst (TWC), Diesel Oxidation Catalyst (DOC), Cu-Z Selective Catalytic Reduction (SCR), Fe-Z SCR and V SCR, Lean NOx Trap (LNT), Ammonia Oxidation Catalyst (AMOx) and Natural Gas Oxidation Catalyst (NGOx).