Novel thermostable chimeric nucleic acid polymerases and methods for their generation and use are disclosed. It is shown that these chimeric nucleic acid polymerases, such as DNA polymerases, can be constructed using enzymatically active domains, isolated from different proteins or chemically synthesized. It is demonstrated that chimeric nucleic acid polymerases of the present invention possess the chemical and physical properties of their component domains (e.g., exonuclease activity, thermostability) and that the chimeric polymerases are thermostable.