Microexpressions are swift, involuntary facial movements that reveal genuine emotions that people may attempt to conceal. These expressions differ from macroexpressions, which are more pronounced or more unmistakable. Subtle emotions are low-intensity, nuanced feelings that may not be overtly expressed or easily recognised. These last for a fraction of a second, making them difficult to detect. Microexpressions and subtle emotions can indicate concealed emotions, making them beneficial for mental health assessments, security inspection, lie detection, and understanding social interactions. Both are universal across nations, cultures and sometimes even in individuals, and may reveal emotions even when someone tries to obscure them. AI-based detection of these emotions relies on a combination of sophisticated feature extraction, deep learning, multimodal data integration, and access to rich, annotated datasets, delivering high accuracy and real-time performance for both research and commercial applications. Various approaches and techniques exists that can be used to detect microexpressions and subtle emotions. Artificial Intelligence bridge the gap between emotional credibility and technological reconstruction, which results in more successful facial reconstruction or recognition. The use of artificial intelligence to investigate subjects microexpressions and subtle emotions has expanded the capabilities of investigation and criminal profiling. Besides criminal investigation, other fields such as customer service, deceit detection, psychotherapy, and human–computer interaction may also utilise this technology. In this chapter, the integration of AI into microexpression and subtle emotion detection is a significant leap forward, offering a powerful tool. As research and development continue, enhanced understanding of human behaviour and improved interactions across diverse applications are promised by AI-driven emotion recognition.