Deep learning (DL) has reshaped the landscape of medical imaging by enabling automated, scalable, and high-accuracy analysis across diverse clinical modalities including MRI, CT, PET/SPECT, ultrasound, Xray, and digital pathology. Early convolutional neural networks (CNNs) established the foundation for tasks such as segmentation, detection, classification, and registration by learning hierarchical spatial representations directly from raw images. Subsequent architectural innovations particularly attention mechanisms, hybrid CNN-attention models, and transformer-based encoders have significantly improved the modeling of long-range dependencies, multi-scale anatomical structures, and complex clinical patterns. Neural architecture search (NAS) has further advanced the field by automating the design and optimization of medical AI systems, leading to architectures that are more efficient, adaptive, and robust. Parallel progress in self-supervised learning and generative modeling, including masked autoencoding, contrastive learning, GANs, VAEs, and diffusion models, has reduced the dependence on large annotated datasets while improving representation quality, modality translation, superresolution, and data augmentation. Multi-modal fusion techniques now enable the integration of imaging, clinical variables, and genomics, supporting more holistic and patient-specific decision making. However, significant challenges persist in clinical deployment, including domain shift, acquisition variability, data imbalance, uncertainty quantification, fairness, out-of-distribution detection, and regulatory requirements for safety and interpretability. This chapter presents a comprehensive overview of these advances, covering foundational principles, architectural evolution, generative and self-supervised paradigms, robustness and generalization strategies, and applications across neuroimaging, oncology, cardiology, abdominal and gastrointestinal imaging, ophthalmology, and pathology. Finally, emerging directions such as foundation models, federated learning, harmonization, and digital-twin frameworks are discussed as key enablers of next generation medical AI systems that are reliable, equitable, and clinically meaningful.