... 10-12, wherestring field theory is discussed. These chapters are still rather introductory, sincemany problems still remain in formulating interacting string field theory, even in thelight-cone formalism. ... gauge-covariant theory then follows in a straight-forward way. String perturbation theory is discussed in chapt. 9.Finally, the methods of chapts. 2-4 are applied to strings in chapts. 10-12, wherestring ... devote chapts. 2-4 to a general study of field theory. Rather than trying to describe strings in the language of old quantum field theory, we recast the formalism of field theory in a mold prescribed...