Transcription activator-like effector (TALE) nucleases (TALENs) have recently emerged as a revolutionary genome editing tool in many different organisms and cell types. The site-specific chromosomal double-strand breaks introduced by TALENs significantly increase the efficiency of genomic modification. The modular nature of the TALE central repeat domains enables researchers to tailor DNA recognition specificity with ease and target essentially any desired DNA sequence. Here, we comprehensively review the development of TALEN technology in terms of scaffold optimization, DNA recognition, and repeat array assembly. In addition, we provide some perspectives on the future development of this technology. Biotechnol. Bioeng. 2013; 110: 1811-1821. (c) 2013 Wiley Periodicals, Inc.