Provided are isolated polynucleotides, polypeptides encoded thereby, nucleic acid constructs comprising same, plant cells and plants comprising same and methods of generating plants with increased yield, biomass, growth rate, vigor, oil content, fiber yield, fiber quality, abiotic stress tolerance, and/or nitrogen use efficiency, wherein the polynucleotides encode polypeptides at least 80% identical to SEQ ID NO: 574-930, 6266-10549 or 10550, such as the polynucleotides set forth in SEQ ID NOs: 1-573, and 931-6265.