The present disclosure provides compositions, methods, kits, systems and apparatus that are useful for nucleic acid polymerization. In particular, modified polymerases and biologically active fragments thereof, such as modified Taq polymerases, are provided that allow for improved nucleic acid amplification. In some aspects, the disclosure provides modified polymerases having improved thermostability, accuracy, processivity and/or read length as compared to a reference Taq polymerase. In some aspects, the disclosure relates to modified polymerases or biologically active fragments thereof, useful for amplification methods, and in practically illustrative embodiments, emulsion PCR.