Provided are isolated polypeptides which are at least 80% homologous to SEQ ID NOs: 710-1153 and 9276-15726, isolated polynucleotides which are at least 80% identical to SEQ ID NOs: 1-709 and 1157-9275, nucleic acid constructs comprising same, transgenic cells expressing same, transgenic plants expressing same and method of using same for increasing yield, abiotic stress tolerance, growth rate, biomass, vigor, oil content, photosynthetic capacity, seed yield, fiber yield, fiber quality, fiber length, and/or nitrogen use efficiency of a plant.