Bagging Predictors, Leo Breiman, 1996Machine Learning, Vol. 24DOI: 10.1007/BF00058655 - Original paper introducing the bagging technique to reduce variance in predictive models.
The Elements of Statistical Learning: Data Mining, Inference, and Prediction, Trevor Hastie, Robert Tibshirani, and Jerome Friedman, 2009 (Springer) - Comprehensive textbook covering theoretical foundations of statistical learning, including detailed sections on ensemble methods like bagging, boosting, and random forests. 2nd edition.
Random Forests, Leo Breiman, 2001Machine Learning, Vol. 45DOI: 10.1023/A:1010933404324 - Original paper introducing the Random Forest algorithm, which extends bagging with feature randomization.