To develop intelligent systems that reflect human abilities, it is crucial to first understand the brain that inspires them. This chapter examines the brain’s evolution, structure, and learning mechanisms, offering key insights into how biological intelligence functions. It provides the foundational knowledge needed to appreciate the principles underlying human cognition. The discussion begins by comparing the brain’s performance and energy efficiency with artificial systems, followed by an overview of its evolutionary development from primitive nerve nets to the complex mammalian brain. The chapter then explores the brain’s functional organization, highlighting key regions such as the cerebellum, hippocampus, thalamus, limbic system, and especially the neocortex, which supports advanced functions like reasoning and voluntary movement. The global structure of the neocortex, its cortical areas, and the brain’s reward system are also examined. Subsequent sections cover neuronal processing, including the structure of neurons, action potentials, synaptic plasticity, and the formation and loss of memory, alongside patterns of human learning and forgetting. The chapter concludes by describing how the brain manages and filters sensory information through interconnected memory systems and sensory modalities, ensuring cognitive efficiency. A summary of the main ideas presented is provided in the final section.