Over the past five years there has been growing interest regarding the impact of lightning NOx (LNOx) emissions on ozone production above North America, especially during the summertime. This interest began when global scale chemical transport models indicated that large quantities of LNOx could accumulate in the upper tropospheric anticyclone that forms above central North America each summer. Over many days the LNOx could react photochemically to produce strong ozone enhancements in the upper troposphere. Observational evidence from the 2004 INTEX Ozonesonde Network Study (IONS), plus measurements from a lidar and commercial aircraft showed that an upper tropospheric ozone enhancement does indeed exist above the southern USA during summer, with LNOx being the most likely contributor. A follow-up IONS ozonesonde campaign in 2006 demonstrated that the ozone enhancement recurs each year with its strength and location being closely tied to the strength and position of the upper tropospheric anticyclone and the associated North American summer monsoon flow. However, large uncertainty still remains regarding the quantity of LNOx produced above North America, with related uncertainties regarding upper tropospheric ozone production efficiency. This talk will review the most recent published findings on this topic, from both an observational and modeling perspective, as well as provide new results describing a North American LNOx transport climatology.