This book introduces novel purification technology for the complex oligonucleotide libraries. Since the concept of synthesizing oligonucleotides (oligos) has been proposed, research fields such as nucleic acid-based therapies (CRISPR-Cas9, DNA/RNA vaccines, RNAi), synthetic biology, protein engineering, and DNA-based data storage have bloomed. The COVID-19 pandemic underscores the potential of nucleic acid-based technologies, such as vaccines or diagnostics. As they emerge as the most promising weapons against the current pandemic, increasing need for highly accessible nucleic acid purification technologies is expected. To meet this demand, an oligo purification technology that can be applied to complex oligo libraries and can purify oligos with single-base resolution is developed. In addition, the purification technology can be applied to highly complex oligo libraries of different lengths, enabling the simultaneous purification of complex oligo libraries with different lengths. The proposed technology can be easily accessed by users and would help accelerate numerous research fields that utilize oligos as fundamental building blocks.