Ensemble learning and data fusion techniques play a crucial role in modern machine learning, enhancing predictive performance, robustness, and generalization. This paper provides a comprehensive survey of ensemble methods, covering foundational techniques such as bagging, boosting, and random forests, as well as advanced topics including multiclass classification, multiview learning, multiple kernel learning, and the Dempster–Shafer theory of evidence. We present a comparative analysis of ensemble learning and deep learning, highlighting their respective strengths, limitations, and synergies. Additionally, we examine the theoretical foundations of ensemble methods, including bias–variance trade-offs, margin theory, and optimization-based frameworks, while analyzing computational trade-offs related to training complexity, inference efficiency, and storage requirements. To enhance accessibility, we provide a structured comparative summary of key ensemble techniques. Furthermore, we discuss emerging research directions, such as adaptive ensemble methods, hybrid deep learning approaches, and multimodal data fusion, as well as challenges related to interpretability, model selection, and handling noisy data in high-stakes applications. By integrating theoretical insights with practical considerations, this survey serves as a valuable resource for researchers and practitioners seeking to understand the evolving landscape of ensemble learning and its future prospects.

Machine learning has become indispensable across various domains, yet understanding its theoretical underpinnings remains challenging for many practitioners and researchers. Despite the availability of numerous resources, there is a need for a cohesive tutorial that integrates foundational principles with state-of-the-art theories. This paper addresses the fundamental concepts and theories of machine learning, with an emphasis on neural networks, serving as both a foundational exploration and a tutorial. It begins by introducing essential concepts in machine learning, including various learning and inference methods, followed by criterion functions, robust learning, discussions on learning and generalization, model selection, bias–variance trade-off, and the role of neural networks as universal approximators. Subsequently, the paper delves into computational learning theory, with probably approximately correct (PAC) learning theory forming its cornerstone. Key concepts such as the VC-dimension, Rademacher complexity, and empirical risk minimization principle are introduced as tools for establishing generalization error bounds in trained models. The fundamental theorem of learning theory establishes the relationship between PAC learnability, Vapnik–Chervonenkis (VC)-dimension, and the empirical risk minimization principle. Additionally, the paper discusses the no-free-lunch theorem, another pivotal result in computational learning theory. By laying a rigorous theoretical foundation, this paper provides a comprehensive tutorial for understanding the principles underpinning machine learning.