The adequate assessment of substance use patterns is essential for identifying substance use disorders, planning interventions, and designing prevention programs for such disorders. Assessment instruments, including standardized questionnaires, assessment scales, and structured interviews, are presented with emphasis on their validity and reliability, as well as their clinical and research applications. The analysis highlights their utility in identifying harmful use patterns and assessing the effectiveness of interventions. Challenges in assessment are also discussed, such as biases in self-reporting and cultural variations, alongside the integration of digital technologies. Ethical and legal considerations are emphasized, including the importance of informed consent, privacy protection, and data confidentiality, in compliance with legal regulations.