Phosphorus deficiency is a serious threat to crop production around the globe. Plant species and even cultivars within species vary greatly in P efficiency. This variation in P efficiency is greatly influenced by different parameters, growth medium and environment. The basic knowledge of P efficiency mechanisms would be helpful for plant breeders to produce P efficient cultivars. The research project comprised of four separate experiments focusing on three major objectives i) study differential response of wheat genotypes under P stress; ii) compare P efficiency calculation methods; and iii) yield contributing parameters under P stress in glasshouse and in field conditions. Wheat genotypes were evaluated for total P, seeds phytate P fraction, various growth, physiological and yield related attributes in series of nutrient solution and soil culture experiments under wire house and field environments. First study (focussed on seeds total P and phytate P fractions) revealed that genotype Inqlab-91 had maximum total P in grains (8.9 mg g-1) and pre-green revolution genotypes accumulated low phytate P in seeds (averaged 1.8 mg g-1) as compared to post-green revolution genotypes (averaged 3.5 mg g-1). During second study, different classification methods/systems for selecting genotypes against P tolerance were compared. To accommodate more number of parameters according need and focus of the researcher a modified P efficiency calculation method was developed. In another study, we compared P efficiency in glasshouse and field conditions. There were significant variations in growth behavior of cultivars in glasshouse and field conditions. Highest P utilization efficiency under glasshouse condition was observed in cultivar Sandal (96.7%) while under field condition highest P utilization efficiency was observed in cultivar Inqilab-91 (86.4%). In last study, we compared different parameters and observed that parameters like grain yield, shoot dry matter, root dry matter, P uptake, tissue P concentration, number of productive tillers, spikelet per spike, grain weight, and harvest index were found responsible for P efficiency. As a whole, genotypes/cultivars Dirk, MaxiPak-65, Blue Silver, Chakwal-86, SH-02 and Darabi-11 were found efficient in P efficiency/tolerance and could be used in future farming while genotypes/cultivars Pari-73, Sandal-73, Wadanak-83, Iqbal-2000 and Seher-06 were found in-efficient in P efficiency. Genotype SH-02 was efficient in P acquisition and genotype Iqbal-2000 was in-efficient in P acquisition. This project will serve as base for plant breeders in selecting wheat genotypes by choosing suitable method of P efficiency calculation, growth medium and parameters responsible for P efficiency mechanisms.