On the Identification of Causal Effects, Jin Tian, Judea Pearl, 2003Journal of Machine Learning Research, Vol. 4 (Department of Computer Science, University of California, Los Angeles / UCLA Cognitive Systems Laboratory) - Introduces the complete ID algorithm for nonparametric identification of causal effects in arbitrary DAGs with hidden variables.
Causal Inference: What If, Miguel A. Hernán and James M. Robins, 2020 (CRC Press)DOI: 10.1201/9781351220491 - A widely referenced textbook covering various identification strategies, including those with unmeasured confounding, and discussing the assumptions underlying different methods.