Elevated [CO2] (e[CO2]) often increases biomass and yield in C3 plants due to an increase in photosynthesis and a decrease in photorespiration. There are two phenomena which limit the positive impact of e[CO2] on crop yield and quality, which will be considered in this review. They are: (a) photosynthetic acclimation to e[CO2] (PAC) and (b) E[CO2] induced N deficiency (eCIND). Understanding PAC and eCIND will be important for ensuring global food supply in future atmospheric conditions, in which [CO2] is expected to rise. In this review, we describe PAC and eCIND on a qualitative and quantitative level, with an emphasis on the many meta-analyses on the subject that have been recently conducted. For PAC, we introduce the various methods that it is quantified and conduct an in-depth discussion of the hypotheses as to the mechanisms which lead to PAC on both a macro and molecular level. Various methods for amelioration of PAC are discussed. For eCIND, we review the various effects of this phenomenon on human and natural systems. We then discuss the various hypotheses as to the mechanisms leading to eCIND. Long term natural processes which may ameliorate or exacerbate eCIND are discussed, and methods for ameliorating are presented. Finally, the connection between eCIND and PAC are analyzed, and future directions for research and agricultural policy are suggested.