This book provides a comprehensive comparison of thermoformed and 3D printed aligners in orthodontic treatment. Through an extensive literature review spanning from 2008 to 2024, ten relevant studies were identified, including randomized controlled trials, observational studies, experimental studies, and comparative analyses. The findings indicate that both types of aligners demonstrate comparable effectiveness in achieving desired tooth movement and occlusal outcomes. However, some studies suggest that 3D printed aligners may offer advantages in terms of precision of fit and customization. This book explores various parameters influencing aligner performance, evaluates the quality of existing studies, and discusses potential implications for clinical practice. Further research is necessary to determine the optimal selection criteria for aligner fabrication methods based on individual patient needs and treatment goals.