Abstract Facial Expression Recognition (FER) has become increasingly relevant in engineering applications spanning security, healthcare, human-robot interaction, and intelligent systems. Accurate recognition of emotional states through facial cues is particularly important for enabling autonomous systems to interpret human intent in dynamic environments. This study presents a survey of recent advances in FER, with a focus on machine learning (ML) and deep learning (DL) methodologies developed between 2019 and 2024. Special attention is given to Facial Action Unit Detection (FAUD) as an intermediate and physiologically grounded representation for expression recognition. The analyzed literature is organized according to the final scope of the proposed models, distinguishing FAUD-oriented, FER-oriented, AU-assisted FER, and FAUD-to-FER approaches. Through this structured comparison, the survey identifies methodological trends, reported performance patterns, and the conditions under which FAUD-based intermediate modeling appears particularly advantageous for reliable FER. Author information Authors and Affiliations Corresponding authors Ethics declarations Competing interests The authors declare no competing interests. Informed consent Informed consent was obtained from all individual participants included in the study. Additional information Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Appendices Appendix A: Supplementary tables Appendix B: Acronyms For quick reference, the following list summarizes the acronyms defined in the main body of the manuscript. | Acronym | Meaning | |---|---| | ABAW | Affective Behavior Analysis in-the-Wild | | AFEW | Acted Facial Expressions in-the-Wild | | AI | Artificial Intelligence | | ANN | Artificial Neural Network | | APM | Attentive Pooling Module | | AU | Action Unit | | BN | Bayesian Network | | BP4D | Binghamton–Pittsburgh 4D Spontaneous Facial Expression Database | | CNN | Convolutional Neural Network | | CV | Computer Vision | | CVPR | IEEE/CVF Conference on Computer Vision and Pattern Recognition